Replaced old lead acid batteries with LifePO4 for home power system off grid

So I finally got around to replacing my ancient 35000 watt hours of LA batteries with about 30000 watt hours of LifePO4. What a major change this is! It over doubled my usable watt hours even though the total bank has less.  With LA cells I could only use about 25-30% with the new LifePo4 I can use 60%. Voltage sag is more or less a thing of the past. With a full system load the voltage only sagged 0.1 volt with my old bank under full load it was over 1.0 volt of sag.

Simply amazing!!!

Certainly sounds like a winner. In your specific situation,  did you compile a direct cost comparison between the two battery types? I'd love to see the numbers if possible,  while still keeping the vast performance improvement in the back of my (rapidly shrinking) mind. Thanks for this post, it helps to shape  my decisions

For the combination of home energy, farmyard vehicle propulsion, and potentially future EV purchase, I continue to try to keep up with developments in solar energy and storage.  While very tempted to sink money into LiFePO4, I'm more inclined to spend only 'dabbling' amounts of cash here and wait to see where battery storage is heading.  So much change in the battery industry and with sodium ion battery technology moving quickly, that may turn out to be a less costly and more eco-friendy option in the near future.  Wife uses an electric Polaris 4X4 Ranger for farm chores and we are sticking with lead acid for the time being, but I will likely test LiFePO4's in my electric golf cart which also is a farmyard 'go-fer' vehicle. As we reside not far from the Canadian border in the northern Plains (USA), I was very encouraged by a bar-stool discussion this past week with a gal from Germany.  She was mentioning her family farm in a mid-central location of that country where she had helped her father install a solar system that is grid-tied, yet supplying a good portion of their home power.  Germany has a decent committment to solar and likley subsidizes these installations (??), but I'm not sure about that.  At any rate, successes in northern regions have me still leaning towards solar integration (or stand-alone?) with grid for our remaining days here.  Just seems from my limited experience so far with that technology to be extremely under-utilized at this point.

Rico Loma wrote:Certainly sounds like a winner. In your specific situation,  did you compile a direct cost comparison between the two battery types? I'd love to see the numbers if possible,  while still keeping the vast performance improvement in the back of my (rapidly shrinking) mind. Thanks for this post, it helps to shape  my decisions

No when I bought these last year my thinking was if I treat them right they would be the last batteries for home power I'll ever need to buy as they will in all likely hood out live me! They were rated for 8000 full cycles or roughly 22 years. Then after much research I had also determined that keeping the battery cells between 20 and 80 percent would double and maybe even triple the lifespan. So now we are talking 16,000-24,000 cycles or days. Well there are 365 days in a year and 16,000 divided by 365 that's roughly 43.5 years and I feel I'll be lucky if I live another 25-30 years....  These are Eve 280AH cells and I have 32 of them in a 16s2p arrangement. I also got them on sale with free shipping for under $4,000. To me that's a no brainer as $4,000 would barely pay a power bill for 3 years for a small extremely efficient house.

I purchased them from the 18650 battery store.

You hit the 16 d nail on the head. That was exactly the type of thinking I hoped for, so thanks Larry

I have 1500+-ah of series/parallel 24 volt L-16 type lead acid US Batteries. No grid here anywhere close.
Looking at Battle Born's website, for American tech, I would likely need about 15,000USD worth of heated batteries, to replace them. Mine cost, in 2023, about 2600USD through Oasis Montana, no sales tax, picked them up in Missoula, no freight.
LA batteries, for all their apparent shortcoming are:
Stone
Axe
Simple.
....and pretty dang heavy.
Been around for well over a hundred years. I'm not sure I want a battery that takes it's own brain to function, even if that brain is American made.
We leave our home 4-6 weeks in the early winter, the temps inside get down to about 10F.  Therefore the self heating batteries. Our winter sun is actually decent. My snow covered yard opens to the south, our lake freezes/snows over. One big reflector. Solar panels work better in the cold.
You could spend less for LiFePo I'm sure. But if you told me you believe the circuitry and safety features of some cut rate Chineese battery you bought on TEMU/AliBaba/Amazon, for which you will have NO recourse in 2-4 years, were equivalent to the units sold by a Nevada based company, I would say my belief is you are delusional. In my mind because of complexity and 'newness' of tech, the lithium is not yet close to proven.
Go to the Battle Born website and look at the list of tests and compliances they subject their batteries to and provide the same data for the batteries you seem to want to recommend to me.
I may or may not not get 3000 cycles to death a LiFePo battery seems to promise, but I never run my batteries to less than 70%, and the 4v lead beasts these batteries replaced lasted about 30 years. I don't kid myself that these batteries are the equivalent of the 4V KWatts we had, but I also could apparently replace my US Batteries like 5-6 times before the cost breakeven for lithium is approached.
My only caution for a high capacity LA like these is to mind the charge rate they like for bulk charging. These batteries like almost 40A of charge to begin.
300W panels are cheap, charge controllers and cabling are not, doing that on a budget is tough, possibly not having to panel up is a plus for lithium. Some of the current charge controllers or control/inverter options no longer support three stage LA charging, something else to consider.
Battery prices in Canada are quite high. I can buy in the States and pay the 10% duty and come out money ahead, even with currency conversion.
When your lithium batteries are 15 years old you can tell me how wonderful they are/have been.
I'll be waiting/listening.

Tommy Bolin wrote:I have 1500+-ah of series/parallel 24 volt L-16 type lead acid US Batteries. No grid here anywhere close.
Looking at Battle Born's website, for American tech, I would likely need about 15,000USD worth of heated batteries, to replace them. Mine cost, in 2023, about 2600USD through Oasis Montana, no sales tax, picked them up in Missoula, no freight.
LA batteries, for all their apparent shortcoming are:
Stone
Axe
Simple.
....and pretty dang heavy.
Been around for well over a hundred years. I'm not sure I want a battery that takes it's own brain to function, even if that brain is American made.
We leave our home 4-6 weeks in the early winter, the temps inside get down to about 10F.  Therefore the self heating batteries. Our winter sun is actually decent. My snow covered yard opens to the south, our lake freezes/snows over. One big reflector. Solar panels work better in the cold.
You could spend less for LiFePo I'm sure. But if you told me you believe the circuitry and safety features of some cut rate Chineese battery you bought on TEMU/AliBaba/Amazon, for which you will have NO recourse in 2-4 years, were equivalent to the units sold by a Nevada based company, I would say my belief is you are delusional. In my mind because of complexity and 'newness' of tech, the lithium is not yet close to proven.
Go to the Battle Born website and look at the list of tests and compliances they subject their batteries to and provide the same data for the batteries you seem to want to recommend to me.
I may or may not not get 3000 cycles to death a LiFePo battery seems to promise, but I never run my batteries to less than 70%, and the 4v lead beasts these batteries replaced lasted about 30 years. I don't kid myself that these batteries are the equivalent of the 4V KWatts we had, but I also could apparently replace my US Batteries like 5-6 times before the cost breakeven for lithium is approached.
My only caution for a high capacity LA like these is to mind the charge rate they like for bulk charging. These batteries like almost 40A of charge to begin.
300W panels are cheap, charge controllers and cabling are not, doing that on a budget is tough, possibly not having to panel up is a plus for lithium. Some of the current charge controllers or control/inverter options no longer support three stage LA charging, something else to consider.
Battery prices in Canada are quite high. I can buy in the States and pay the 10% duty and come out money ahead, even with currency conversion.
When your lithium batteries are 15 years old you can tell me how wonderful they are/have been.
I'll be waiting/listening.

If we are all still around in 15-30 years I'll be happy to.

I built my system from parts so I can also replace parts as needed IE: the BMS / brain if it goes bad

It got down to about 20f last night and I never insulated or heated the batteries. Lost power about 2:30am took till about noon to get the cells warmed up to about 35f or 2c and got power back online. Spent the better part of the day after that wrapping the cells with heat tape for pipes and put insulation under and over , still need to go back and insulate the sides. Used 30 feet of heat tape with a 90w draw. It has it's own thermostat on at 35 off at 50 if I remember correctly.

Larry, that is an interesting problem to have.
I have heard of it but I dont live where it gets that cold.
Is there some system to ensure they do not chill down?

larry kidd wrote:It got down to about 20f last night and I never insulated or heated the batteries. Lost power about 2:30am took till about noon to get the cells warmed up to about 35f or 2c and got power back online. Spent the better part of the day after that wrapping the cells with heat tape for pipes and put insulation under and over , still need to go back and insulate the sides. Used 30 feet of heat tape with a 90w draw. It has it's own thermostat on at 35 off at 50 if I remember correctly.

That's good to know. I thought lithium batteries would just not charge at low temps. I didn't know discharging would be affected as well. My batteries are in the same insulated enclosure as my inverter and it seems like the inverter puts off enough heat to keep the battery above warm.

larry kidd wrote:It got down to about 20f last night and I never insulated or heated the batteries. Lost power about 2:30am took till about noon to get the cells warmed up to about 35f or 2c and got power back online. Spent the better part of the day after that wrapping the cells with heat tape for pipes and put insulation under and over , still need to go back and insulate the sides. Used 30 feet of heat tape with a 90w draw. It has it's own thermostat on at 35 off at 50 if I remember correctly.

Living where we do in the central US just below the Canadian border, an experience like this is what causes me to hesitate on diving into LiFePO4.  I probably will anyway and just keep the investment small to modest.  Wife is still tooling around the farmyard with recent ~10 degree F using lead-acid batteries in a Polaris Ranger EV and we are grateful for the robustness of the time-tested tech, even with the known power deficits of these batteries in cold weather.

There was mention recently of Canada leaning more towards solid-state/sodium ion technology, partially because it may be a less expensive battery to produce, but also in large part due to its greater resiliency to cold temperatures.  Still that battery too will use a battery management system (BMS) and one hopes these don't turn out to be a weak link in the technology.  Larry K, I always wondered if a seedling heating mat would be enough to prevent severe temperature drop in such situations.  CLearly if the location is too cold and the batteries unprotected, the BMS will do best to shut down the battery.  But in situations where the batteries are housed in an insulated container of sorts, a seedling mat seems to be designed to produce low temperature, low wattage heat to the item(s) sitting on the mat.  Perhaps this would be a safe solution for many out there?   Also a question for those having installed LiFePO4 batteries going back a decade or two:  Have you experienced or heard of situations where either the cells or the BMS itself failed causing need for battery or cell replacement? If the BMS goes bad and the cells are otherwise good, can the BMS be replaced (assuming a battery case whose contents can be accessed) fairly easily?  Thanks!

John Weiland wrote:

larry kidd wrote:It got down to about 20f last night and I never insulated or heated the batteries. Lost power about 2:30am took till about noon to get the cells warmed up to about 35f or 2c and got power back online. Spent the better part of the day after that wrapping the cells with heat tape for pipes and put insulation under and over , still need to go back and insulate the sides. Used 30 feet of heat tape with a 90w draw. It has it's own thermostat on at 35 off at 50 if I remember correctly.

Living where we do in the central US just below the Canadian border, an experience like this is what causes me to hesitate on diving into LiFePO4.  I probably will anyway and just keep the investment small to modest.  Wife is still tooling around the farmyard with recent ~10 degree F using lead-acid batteries in a Polaris Ranger EV and we are grateful for the robustness of the time-tested tech, even with the known power deficits of these batteries in cold weather.

There was mention recently of Canada leaning more towards solid-state/sodium ion technology, partially because it may be a less expensive battery to produce, but also in large part due to its greater resiliency to cold temperatures.  Still that battery too will use a battery management system (BMS) and one hopes these don't turn out to be a weak link in the technology.  Larry K, I always wondered if a seedling heating mat would be enough to prevent severe temperature drop in such situations.  CLearly if the location is too cold and the batteries unprotected, the BMS will do best to shut down the battery.  But in situations where the batteries are housed in an insulated container of sorts, a seedling mat seems to be designed to produce low temperature, low wattage heat to the item(s) sitting on the mat.  Perhaps this would be a safe solution for many out there?   Also a question for those having installed LiFePO4 batteries going back a decade or two:  Have you experienced or heard of situations where either the cells or the BMS itself failed causing need for battery or cell replacement? If the BMS goes bad and the cells are otherwise good, can the BMS be replaced (assuming a battery case whose contents can be accessed) fairly easily?  Thanks!

John there is Lithium and then there is lithium... Most of the server rack type assemblies are available with a built in heating mat. It is a little annoying though as it will only power up while the batteries are charging and cannot be used in an off grid discharge only scenario. I have taken to oversizing my insulating boxes by 6 inches on all sides and incorporate a 300 watt heater with a blower. Even with the extra troubles lithium is worth it. The greatest advantage is rate of charge. Traditionally you would limit your array size to match the ideal rate of charge of a lead acid battery since the rest was "wasted". Now we can oversize the array so that you can grab 100 percent of available sun on those days where the sun comes out hard for short amounts of time. Also all that extra time running a generator for absorb charging is also a thing of the past. So the little power you use heating the box is worth it. I would suggest sticking to a company that has distribution and available spare parts like all high cost tech items. I like the units that do closed looped communication with the inverter so you get a real time temp reading and balanced charging. The cheap drop in replacements without comms have not been doing well long term. As to Sodium they are starting to show up but are in their early adopter high cost unknown specs days so I'll wait for now.
Cheers,  David

I was really excited about Sodium ion until I realized the way they work all the way across the voltage. Where as most equipment is set for the small voltage range of lead acid cells. LifePO4 also uses a fairly small range L-ion uses a larger range and sodium uses almost the entire voltage from 2 past 12 on a 12 volt system. To put this further in context a lead battery at full charge 12.7V down to about 12 volts if you want any kind of battery life. While the system can go down to maybe 10 volts it will kill a lead battery quick fast and in a hurry. Look at the range on sodium to see what I'm talking about. This will require largely different equipment for sodium from lead acid.

larry kidd wrote:I was really excited about Sodium ion until I realized the way they work all the way across the voltage. Where as most equipment is set for the small voltage range of lead acid cells. LifePO4 also uses a fairly small range L-ion uses a larger range and sodium uses almost the entire voltage from 2 past 12 on a 12 volt system. To put this further in context a lead battery at full charge 12.7V down to about 12 volts if you want any kind of battery life. While the system can go down to maybe 10 volts it will kill a lead battery quick fast and in a hurry. Look at the range on sodium to see what I'm talking about. This will require largely different equipment for sodium from lead acid.

Yes, this seemed to be an aspect of sodium ion batteries that was not receiving as much attention.  Certainly it **seems** from several sources that the battery industry is gearing up a lot of sodium ion battery production, .... but are they waiting for the roll-out to drop the other shoe??--- That a buyer will have to re-tool much of their whole system to adapt to the power curve of sodium ion batteries?  Would be curious to know other's thoughts here...

Also, my impression is that 48V battery systems are winning out in the popularity battle for alt-energy based systems for home, cabins, etc.  Yet I can see advantages of 24V systems...especially with LiFePO4 batteries....when considering weight and safety.  In my case, I'm potentially looking at a 10 kW hybrid inverter/charger with solar, but initially only for a few critical items like well pump and propane furnace and a few light circuits. Only rarely would the batteries be drawn down to 50% with ample anticipated time to recharge before needing again.  The inverter system and batteries would be wall-mounted in a basement ranging from 50F to 65F winter to summer and ~2 kW of solar PV capacity used for charging. About 30 ft of cabling would separate the PV panels from an MPPT charge controller. So to be clear, this would be an introductory backup system for when grid power failure occurs.  Is there some reason that for such a system I should go with 48V instead?  Thanks!

John Weiland wrote:

larry kidd wrote:I was really excited about Sodium ion until I realized the way they work all the way across the voltage. Where as most equipment is set for the small voltage range of lead acid cells. LifePO4 also uses a fairly small range L-ion uses a larger range and sodium uses almost the entire voltage from 2 past 12 on a 12 volt system. To put this further in context a lead battery at full charge 12.7V down to about 12 volts if you want any kind of battery life. While the system can go down to maybe 10 volts it will kill a lead battery quick fast and in a hurry. Look at the range on sodium to see what I'm talking about. This will require largely different equipment for sodium from lead acid.

Yes, this seemed to be an aspect of sodium ion batteries that was not receiving as much attention.  Certainly it **seems** from several sources that the battery industry is gearing up a lot of sodium ion battery production, .... but are they waiting for the roll-out to drop the other shoe??--- That a buyer will have to re-tool much of their whole system to adapt to the power curve of sodium ion batteries?  Would be curious to know other's thoughts here...

Also, my impression is that 48V battery systems are winning out in the popularity battle for alt-energy based systems for home, cabins, etc.  Yet I can see advantages of 24V systems...especially with LiFePO4 batteries....when considering weight and safety.  In my case, I'm potentially looking at a 10 kW hybrid inverter/charger with solar, but initially only for a few critical items like well pump and propane furnace and a few light circuits. Only rarely would the batteries be drawn down to 50% with ample anticipated time to recharge before needing again.  The inverter system and batteries would be wall-mounted in a basement ranging from 50F to 65F winter to summer and ~2 kW of solar PV capacity used for charging. About 30 ft of cabling would separate the PV panels from an MPPT charge controller. So to be clear, this would be an introductory backup system for when grid power failure occurs.  Is there some reason that for such a system I should go with 48V instead?  Thanks!

 

Amperage and wire size / expense!

larry kidd wrote:

John Weiland wrote:...... Is there some reason that for such a system I should go with 48V instead?  Thanks!

 

Amperage and wire size / expense!

So the extra cost of wire size is undertandably a factor.  It also seems like there are fewer offerings for 24V inverter combos that are in the 10 kW output range and perhaps the higher amperage is a factor here as well?  If the wiring run from the PV panels to the MPPT controller and batteries is kept to a minimum -AND- the inverter is within a few feet as well, it's then 120/240V AC beyond this point and now can use the smaller wire, correct?  Certainly, there are many pros with just focusing on 48V systems, but as an aging amateur I'm also inclined to the purported increased safety of 24V and the lighter weight and size of the LiFePO4 batteries being installed.  Don't know if this makes sense or is really just unfeasible or not so logical in the end.....?  Thanks!

John Weiland wrote:

larry kidd wrote:

John Weiland wrote:...... Is there some reason that for such a system I should go with 48V instead?  Thanks!

 

Amperage and wire size / expense!

So the extra cost of wire size is undertandably a factor.  It also seems like there are fewer offerings for 24V inverter combos that are in the 10 kW output range and perhaps the higher amperage is a factor here as well?  If the wiring run from the PV panels to the MPPT controller and batteries is kept to a minimum -AND- the inverter is within a few feet as well, it's then 120/240V AC beyond this point and now can use the smaller wire, correct?  Certainly, there are many pros with just focusing on 48V systems, but as an aging amateur I'm also inclined to the purported increased safety of 24V and the lighter weight and size of the LiFePO4 batteries being installed.  Don't know if this makes sense or is really just unfeasible or not so logical in the end.....?  Thanks!

48V is likely the safest system size for a number of reasons. It is also one of the most power economical due to conversion losses. Over 48vdc and you start needing protection to touch bare connections below it and the amperage gets crazy high and more dangerous. Up through 48vdc handling connections bare handed is fairly safe .

could we not be getting away from all lithium and lead type batteries… on favor of the old orginal superpower:  Nickel-iron?  (a.k.a. “the edison battery”)

Guadagno Attilio-Cesare wrote:could we not be getting away from all lithium and lead type batteries… on favor of the old orginal superpower:  Nickel-iron?  (a.k.a. “the edison battery”)

My understanding is that the nickel in them makes them cost a lot more than the alternatives?  Be happy to be wrong though.

sounds like that would be in alignment with permaculture principles… where we put in alot more effort, upfront, to in-joy the benefits, with little to no effort, perpetually.

Most items in a house can be run with 12 volt batteries.
But the large loads like water heater or welder would work better with 48 volt batteries and inverters.
It might be a good idea to have both a 12 and 48 volt setup.
I think the idle wattage is less on 12 volts. On some 48 volt 12Kwatt inverters the idle wattage can be 100 watts and hour.
But is commonly 50-60 watts on a 48 volt 6K inverter, which is all I'd need.

John Weiland wrote:

larry kidd wrote:
Also, my impression is that 48V battery systems are winning out in the popularity battle for alt-energy based systems for home, cabins, etc.  Yet I can see advantages of 24V systems...especially with LiFePO4 batteries....when considering weight and safety.  In my case, I'm potentially looking at a 10 kW hybrid inverter/charger with solar, but initially only for a few critical items like well pump and propane furnace and a few light circuits. Only rarely would the batteries be drawn down to 50% with ample anticipated time to recharge before needing again.  The inverter system and batteries would be wall-mounted in a basement ranging from 50F to 65F winter to summer and ~2 kW of solar PV capacity used for charging. About 30 ft of cabling would separate the PV panels from an MPPT charge controller. So to be clear, this would be an introductory backup system for when grid power failure occurs.  Is there some reason that for such a system I should go with 48V instead?  Thanks!

A 10kW inverter will draw about 400A at 24V at full load. It will only draw about 200A at 48V. Generally the charge and discharge current for LiFePO4 batteries should not exceed their amp-hour rating. For example, Eve 280AH cells should not be charged or discharged at more than 280A maximum, 140A nominal. You would need multiple battery packs in parallel and some really big wire to support a 400A discharge rate in a 24V system. A 400A disconnect / breaker  would also be required. Charging will not be a problem with a 2kW solar array since it would only charge at about 80A at 24V or 40A at 48V. Keeping the charge current well below the maximum will reduce heating. Excess heat is one of the biggest factors in reducing LiFePO4 battery life.

LiFePO4 batteries will degrade not only as the cycle count increases but also based on their calendar age. The battery capacity will decline over time even if it is not cycled. I hope to get more than 10 years usage at a reduced capacity but the actual longevity of the Eve cells is hard to pin down.

In our off-grid location the winter days are short and often overcast. The backup generator had to run much more often and longer with the prior lead acid battery bank. If lead acid batteries are not fully charged on a regular basis (maybe every 5-7 days?) sulfate will accumulate on the lead plates reducing the battery capacity. They can be over-charged (equalized) to counteract this effect somewhat but it is best to fully charge them on a regular basis. They also require a relatively long absorption time during which the charge current is continually dropping. This means the generator runs a long time at a partial load which is not as fuel efficient as running at full load. In contrast, the LiFePO4 batteries are happy running from 20% to 80% which means the generator does not have to run as often. For example, I might run it for an hour or two in the evening every few days while waiting for a sunny day. If it runs long enough to fully charge the batteries it runs at near full load the whole time since LiFePO4 don't need a long absorb time.

Check out Will Prouse's YouTube channel for his independent battery and equipment test results.

Most people talk about capacity, but the bigger difference is how the system behaves day to day.
With lead acid, once you get past ~80% it barely takes charge, so a lot of solar ends up wasted. LiFePO4 keeps accepting charge almost to the top, so you actually use more of what you generate.
It’s also not just a battery swap — a lot of issues people see (cold weather behavior, charging logic, weird cutoffs) are more about system setup than the chemistry itself. For example, setups like this 48V LiFePO4 system are basically designed around that kind of full-solar usage: https://cmxbattery.com/product/48kwh-lifepo4-solar-battery-51-2v-942ah-300a-bms-home-backup/

Following,,,,,really useful information here for either DIY or planning with a contractor.  And from 'balcony solar' [ https://www.youtube.com/watch?v=gehKnTc0XfQ ] to full off-grid installs, so much variety out there to choose from!

Jackie Lei wrote:Most people talk about capacity, but the bigger difference is how the system behaves day to day.
With lead acid, once you get past ~80% it barely takes charge, so a lot of solar ends up wasted. LiFePO4 keeps accepting charge almost to the top, so you actually use more of what you generate.
It’s also not just a battery swap — a lot of issues people see (cold weather behavior, charging logic, weird cutoffs) are more about system setup than the chemistry itself. For example, setups like this 48V LiFePO4 system are basically designed around that kind of full-solar usage: https://cmxbattery.com/product/48kwh-lifepo4-solar-battery-51-2v-942ah-300a-bms-home-backup/

Hi Jackie,
I do not see on the link anything about UL9540 compatibility or certification in Europe or North America.

David Baillie wrote:

Jackie Lei wrote:Most people talk about capacity, but the bigger difference is how the system behaves day to day.
With lead acid, once you get past ~80% it barely takes charge, so a lot of solar ends up wasted. LiFePO4 keeps accepting charge almost to the top, so you actually use more of what you generate.
It’s also not just a battery swap — a lot of issues people see (cold weather behavior, charging logic, weird cutoffs) are more about system setup than the chemistry itself. For example, setups like this 48V LiFePO4 system are basically designed around that kind of full-solar usage: https://cmxbattery.com/product/48kwh-lifepo4-solar-battery-51-2v-942ah-300a-bms-home-backup/

Hi Jackie,
I do not see on the link anything about UL9540 compatibility or certification in Europe or North America.

Hi, I’m not entirely sure about that either. You may want to double-check directly with the supplier to confirm the UL9540 compatibility or any certifications for Europe or North America.

There has been a bit of talk in this thread about essentially the fear of what happens if the BMS in a lithium battery dies, and if those batteries are a commercial pre-built system, I suppose those concerns are real factors in the decision process. If you build a battery from parts, it's really not an issue, because you can still use the cheapest parts around, but if/when they fail, you can still replace them, you can upgrade them to less cheap parts, or you can replace them with the best quality parts available, now that you have experienced the functionality the battery system has brought to your life.

I'm not a big fan of buying commercial battery systems any more than I'm not a fan of buying a pre-built computer for a specialized use. "If you want a 'gaming' computer, build it to meet the junction of your needs and your budget, don't buy into the marketing of what some sale/marketing team decided would be flashy enough to bump their profit margins...

LiFePO4 batteries have become a commodity item, that's too easy to duplicate with readily available components, that it's hard to justify the extra expense of buying the package, unless you really wanted/needed the convenience of buying it and plugging it in, then quickly moving on to something else. For the same reasons I'd avoid the pre-built 'gaming' computers, manufacturers of battery systems are still for-profit businesses, that will cut corners to appeal to the middle of the bell curve, since that's where the profit is. If you happened to want or need anything just outside of that, you end up compromising your needs, or wasting time/money to do it over just to get it right. DIY doesn't mean that you don't have to do anything over, it just increases the speed with which you can, plus it drops the cost of doing so.

Case in point, last week, I built a LiFePO4 battery that I was & am very happy with, but I wasn't happy with the BMS or the "brains" of the battery. Yesterday, I replaced the old BMS with a much better matched one for my needs and it pretty much just involved using a screwdriver to swap the connections.

Allen Jackson wrote:There has been a bit of talk in this thread about essentially the fear of what happens if the BMS in a lithium battery dies, and if those batteries are a commercial pre-built system, I suppose those concerns are real factors in the decision process. If you build a battery from parts, it's really not an issue, because you can still use the cheapest parts around, but if/when they fail, you can still replace them, you can upgrade them to less cheap parts, or you can replace them with the best quality parts available, now that you have experienced the functionality the battery system has brought to your life.

I'm not a big fan of buying commercial battery systems any more than I'm not a fan of buying a pre-built computer for a specialized use. "If you want a 'gaming' computer, build it to meet the junction of your needs and your budget, don't buy into the marketing of what some sale/marketing team decided would be flashy enough to bump their profit margins...

LiFePO4 batteries have become a commodity item, that's too easy to duplicate with readily available components, that it's hard to justify the extra expense of buying the package, unless you really wanted/needed the convenience of buying it and plugging it in, then quickly moving on to something else. For the same reasons I'd avoid the pre-built 'gaming' computers, manufacturers of battery systems are still for-profit businesses, that will cut corners to appeal to the middle of the bell curve, since that's where the profit is. If you happened to want or need anything just outside of that, you end up compromising your needs, or wasting time/money to do it over just to get it right. DIY doesn't mean that you don't have to do anything over, it just increases the speed with which you can, plus it drops the cost of doing so.

Case in point, last week, I built a LiFePO4 battery that I was & am very happy with, but I wasn't happy with the BMS or the "brains" of the battery. Yesterday, I replaced the old BMS with a much better matched one for my needs and it pretty much just involved using a screwdriver to swap the connections.

Allen, I respect your desire to build the battery you want for a specific application. My issue is when people install non certified gear in their house and expose themselves to all sorts of insurance and mortgage complications because of it. Some areas are more forgiving but a non certified piece of gear become a great way to deny a claim whether it was at fault or not. The good thing is the technology is so much better than even 3 years ago and good safe solutions are common and dropping in price.
Cheers, David

David Baillie wrote:Hi Jackie,
I do not see on the link anything about UL9540 compatibility or certification in Europe or North America.

I haven't seen anything about UL9540 compatibility either, so I started digging...

For the most part, it doesn't matter, and it's NOT applicable!

Let me explain. UL 9540 is the standard, to which energy storage systems are tested.

UL 9540A is the testing method of those systems to determine & evaluate their capacity for thermal runaway in a fire.
(This is used to determine how close they can be to each other, and most of the requirements don't apply to single and 2-family residences)

UL 9540B was developed to specifically address residential energy storage systems.

While UL 9540 is NOT just for lithium ion batteries, it really doesn't have much to say about LiFePO4 batteries. Because it's primarily focused on fire hazards and fire safety, it covers lead acid batteries, which can generate explosive hydrogen gas, and lithium ion batteries, which can be driven into thermal runaway by damage or heat. Since lithium iron phosphate batteries don't exhibit those characteristics, they already inherently pass the basic cell-level test requirements of UL 9540A (or UL 9540B), and per the testing norms, if the cells cannot be driven into thermal runaway, there's no further need to test the module or system that they are installed in.

UL 9540B was driven primarily by California fire code, that became more strict than UL 9540, to focus on the gaps in coverage of residential systems (pretty much due to the rise in popularity of Tesla Powerwalls and Tesla vehicles), because they DO use lithium ion batteries, and are most commonly found in residential settings.

Unless you're planning to install a DIY lithium ion based system the applicable regulatory agencies aren't likely to be paying much attention to your systems, unless there's an outside chance you're looking at a large scale installation of lead acid batteries, because of the hydrogen generation).

The fervor over insurance companies and inspectors not liking LiFePO4 battery systems, is only possible if they are ignorant of the differences between lithium ion and lithium iron phosphate batteries. It's even likely that inspectors will see the word "lithium" and automatically assume that a system is equivalent to a Tesla powerwall. That doesn't mean it can be set on fire, though...

David Baillie wrote:
Allen, I respect your desire to build the battery you want for a specific application. My issue is when people install non certified gear in their house and expose themselves to all sorts of insurance and mortgage complications because of it. Some areas are more forgiving but a non certified piece of gear become a great way to deny a claim whether it was at fault or not. The good thing is the technology is so much better than even 3 years ago and good safe solutions are common and dropping in price.
Cheers, David

Since there's an expense to getting any certification, and those who are aware of the details of the technology realize that lithium ion and lithium iron phosphate are apples and oranges, it may take some time to get relevant folks to push for certification (especially of units that aren't needing certification, but rather might benefit from an "official exemption" to publicly and officially label them as "safe".

In many ways, we're victim to the popularity of Tesla products, that have been proven to not be as safe as they were first thought to be.

The 2023 edition of the NEC doesn't include mention of UL 9540 (I just checked my copy), and UL 9540A & UL 9540B are still very much in development. It's likely that the 2026 edition of the NEC will have more than the 3 pages about energy storage systems than the 2023 edition has, but ultimately, what matters, is the AHJ (authority having jurisdiction) in your local area.

If your local building codes are compliant to the 2017 NEC, then that's what the local inspector will be using... Check your local municipality for what level (if any) that they choose to comply with the national codes.

Edit:  Since the 2026 NEC has already been published and they don't appear to be highlighting any changes in energy storage systems, it's likely that any relevant parts of UL 9540B won't make it into the national code until 2029...  This is a pretty expensive book, so I don't tend to buy the latest one every 3 years when they come out, unless MY local jurisdiction adopts the new version, and city hall doesn't tend to move that fast...  Not sure there's much reason to get the 2026 edition (for me).

David Baillie wrote:
Allen, I respect your desire to build the battery you want for a specific application. My issue is when people install non certified gear in their house and expose themselves to all sorts of insurance and mortgage complications because of it. Some areas are more forgiving but a non certified piece of gear become a great way to deny a claim whether it was at fault or not. The good thing is the technology is so much better than even 3 years ago and good safe solutions are common and dropping in price.
Cheers, David

An insurance company or insurance adjuster is bound by the local codes of the jurisdiction too, and any fire inspector or arson investigator is also using the same local codes to assess any issues that are found. Those codes aren't static, and normally, the process of permitting and inspection will be enough to insure compliance with the codes in place at the time of installation. Even if one is not mandated to get permits or even an inspection for an installation, if the guidelines for the current codes are used, it's hard for an insurance company to rule against the installation.

I'm not at all advocating for poor quality batteries or hazardous installations, but quite the opposite - mainly because it's so easy to do it well and safely too. If there's ANY doubt or question, PLEASE seek expert advice, but knowledge is power, and if folks become aware that they don't have to pay the premium tier pricing to get as good or better results as the well-marketed & usually much more expensive choices, they become better consumers.

Years ago (about 2014-ish?), solar power was really starting to come into its own, and the NEC was lagging. The National Fire Protection Agency was getting terrified about all the roof-mounted solar that was sprouting all over, and successfully made the case for module-level shut down to be mandated. The solar industry screamed about the cost of implementing this change and pointed out that some of the requirements weren't even physically possible (PV panels + daylight = voltage at the panel, and no law could change that...). The NFPA based their demand for module-level shutdown on the scenario of a firefighter needing to chop through a roof in a hurry, to save lives.

By the time the 2017 NEC was released they had regulated module-level shutdown, but added a clause that delayed implementation until Jan 2019. Their requirements were a somewhat unclear and it unfortunately allowed inspectors to go overboard on many aspects of new solar systems. There was a big fuss made over it, and the 2020 NEC was a welcomed revision and clarification, specifically for the sections regarding solar systems. They separated energy storage systems from solar, and they added exemptions for ground-mounted solar arrays, because no firefighter would ever be required to "chop" through a ground mounted solar array in a hurry to save lives.

All this time, my local municipality hadn't ratified anything higher than the 2014 NEC, so while I knew the writing was on the wall, no insurance adjuster could hold me to a higher standard... There were at that same time, plenty of counties that were still using the 2008 NEC. If someplace is claiming a requirement for UL 9540 compliance, it's not the national electric code, (yet?), but rather some local requirement, and possibly an uninformed one that will mature (hopefully quickly) to recognize the science behind the letter of the standard.