Forum:

solar

Testing your homestead battery capacity...

John Weiland

master pollinator

Posts: 3046

Location: RRV of da Nort, USA

1014

posted 3 hours ago

2
Number of slices to send:

Optional 'thank-you' note:

Send

For those that use battery storage for home power generation or even powered small electric vehicles or appliances, do you check the capacity of your batteries annually or every few years? I have a battery load tester to examine general battery health, but for deep cycle batteries that are rated in amp-hours, how to you test for how far off of the original "100%" that your battery capacity has declined? General internet searches have revealed some rather sophisticated devices for which load, discharge rate, etc. can be programmed, but I was wondering if I was missing something that would be more low tech, but still give a duration measurement on when the battery was depleted. Thoughts? Thanks!.....

“The most important decision we make is whether we believe we live in a friendly or hostile universe.”― Albert Einstein

David Baillie

pollinator

Posts: 1016

Location: Central Ontario

221

I like...

posted 3 hours ago

3
Number of slices to send:

Optional 'thank-you' note:

Send

John Weiland wrote:For those that use battery storage for home power generation or even powered small electric vehicles or appliances, do you check the capacity of your batteries annually or every few years? I have a battery load tester to examine general battery health, but for deep cycle batteries that are rated in amp-hours, how to you test for how far off of the original "100%" that your battery capacity has declined? General internet searches have revealed some rather sophisticated devices for which load, discharge rate, etc. can be programmed, but I was wondering if I was missing something that would be more low tech, but still give a duration measurement on when the battery was depleted. Thoughts? Thanks!.....

John, for larger lead acid deep cycle banks i used to apply a c5 to c10 load on the inverter and hold for 15-30 minutes with all inputs and other house loads off. I usually used space heaters. The speed at which the voltage dropped would give me an approximation of ability. You start fully charged with a good absorb cycle and repeat after say a year and see where they are in comparison. Its pretty time consuming and to have someone do it expensive so its kind of gone the way of the dodo bird. Add to that the switch to lithium and its a dying art. Ill still perform a test if someone asks me to evaluate a house they are buying or figuring out if they are going to make the winter.
Cheers, David

John Weiland

master pollinator

Posts: 3046

Location: RRV of da Nort, USA

1014

posted 2 hours ago

1
Number of slices to send:

Optional 'thank-you' note:

Send

Thanks, David! Can you tell me why this is not done routinely for LiFePO4 batteries? Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity. And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located. Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

“The most important decision we make is whether we believe we live in a friendly or hostile universe.”― Albert Einstein

D Nikolls

pollinator

Posts: 1844

Location: Victoria BC

351

posted 1 hour ago

1
Number of slices to send:

Optional 'thank-you' note:

Send

John Weiland wrote:Thanks, David! Can you tell me why this is not done routinely for LiFePO4 batteries? Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity. And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located. Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

I expect it is skipped because it requires some gear and some work..

For me, I am relying on my shunt and Victron Cerbo to do a reasonable job of monitoring energy consumption; if I find that voltage is nearing the low voltage cutoff and the amp-hours consumed since last full charge are not ballpark of what I am expecting, I will investigate individual batteries in the parallel bank.

I do load test and roughly capacity test the budget LiFePO4 batteries I use before putting them in service, but this is a bit of pain as I don't have a spare inverter or a high power DC load available at this time, so it requires installing the new battery as the sole power source, running it down to the inverter cutoff point with space heaters, and then seeing how many amp-hours (from the Victron charge controllers) it takes to reach full charge. Then if all good reconnect the other batteries..

To be honest I rarely look at any of this in the summer half of the year.. it tends to just work, tons of wasted power. Fall is time to check on it before the dark returns..

'Theoretically this level of creeping Orwellian dynamics should ramp up our awareness, but what happens instead is that each alert becomes less and less effective because we're incredibly stupid.' - Jerry Holkins

Mart Hale

pollinator

Posts: 1261

370

I like...

posted 1 hour ago

1
Number of slices to send:

Optional 'thank-you' note:

Send

I don't do capacity tests other than I know what loads I put on the battery and can refer to how much I can know from my past loads how the batteries respond. If they do the loads they need to do, for me that is good enough, I run lithium batteries, and I have created my own wifi battery device that I can record on an open source program domoticz the data.

Screenshot_2026-10-13_14-22-02.png

Life on a farm is a school of patience; you can't hurry the crops or make an ox in two days.
Henri Alain

David Baillie

pollinator

Posts: 1016

Location: Central Ontario

221

I like...

posted 1 hour ago

1
Number of slices to send:

Optional 'thank-you' note:

Send

John Weiland wrote:Thanks, David! Can you tell me why this is not done routinely for LiFePO4 batteries? Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity. And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located. Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

Mart totally wins for geek wizardry! His own monitoring! If I want to test a lithium it depends in the quality of the inverter and the batteries. Those drop in replacements that dont need comms to inverter you would have to charge until it does not take charge, apply a known load and discharge till it shuts down; i dont like that. If its a solark, lux or eg4 ( rebadged lux) and a battery that does two way comms you have a state of charge meter and an app so its way easier. I can apply a known charge to it add in the system running load and watch the percentage go down. If it matches spec you are golden as it ages I would expect it to drop more rapidly. The batteries im installing today are less than 2 years and so far no change over about 12 systems. Here is a screen shot of the lux app: the website version is better. Eg4 and solark have similar ones. The cheaper inverters not so great I dont install them as its too much call backs and confusing menus. There are other good ones of course.

Screenshot_20261013-144659.png

David Baillie

pollinator

Posts: 1016

Location: Central Ontario

221

I like...

posted 58 minutes ago

Number of slices to send:

Optional 'thank-you' note:

Send

John Weiland wrote:Thanks, David! Can you tell me why this is not done routinely for LiFePO4 batteries? Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity. And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located. Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

Please all, and you will please none --Aesop ... displeased tiny ad:

2 decks of gardening and permaculture playing cards - The Purple Deck

https://permies.com/w/cards2