Favorite method for lead acid battery rejuvenation?....

We have a few sealed lead acid batteries that have not been maintained the best....don't know if it's sulfation or something else that's impacting the fact that they won't charge over 85 - 90% capacity, even though only about a year or two old (12V; 12 - 18 Ah).  I've read that one way to try to rejuvenate them is to deep drain and then recharge to full about 5 times in succession but am wondering if others have done this and what the preferred method is to safely discharge to 0% charge.  Any favorite protocols out there for doing this and insights into degrees of success?  Thanks!

Hi John;
Good question!  
I'm not sure if draining a lead acid is proper or not.
A quick look showed them removing the sealed top to add battery acid.
Hopefully, another will reply who has tried this.

To drain a 12 vt mini battery I would hook a 12 vt automotive light bulb directly to the battery.

John Weiland wrote:We have a few sealed lead acid batteries that have not been maintained the best....don't know if it's sulfation or something else that's impacting the fact that they won't charge over 85 - 90% capacity, even though only about a year or two old (12V; 12 - 18 Ah).  I've read that one way to try to rejuvenate them is to deep drain and then recharge to full about 5 times in succession but am wondering if others have done this and what the preferred method is to safely discharge to 0% charge.  Any favorite protocols out there for doing this and insights into degrees of success?  Thanks!

For lead acid there is no memory effect to my knowledge. If they are sealed lead acid not gels then you can usually pop the caps and add some distilled water. Often  people will give them an absorb charge at a flooded voltage and they can boil dry. .

I think for general lead acid battery advice. Rolls battery has a great manual. https://rollsbattery.com/wp-content/uploads/2019/11/Rolls-Battery-User-Manual.pdf

And so much more can be found here. https://support.rollsbattery.com/en/support/solutions

super helpful website.

I believe specific gravity is the only way to tell if the battery is full or not. https://support.rollsbattery.com/en/support/solutions/articles/5964-battery-sulfation

There are some chargers that are designed for battery reconditioning, by sending pulsed charges into the battery to help break up sulfate crystals.  Other than that, for a sealed battery, the only viable option for you is to turn them in for recycling.  

Before you do that though look into the root cause of why they failed in the first place?
Were they sitting there unattended?  Were they undercharged by an inadequate system?  Replacing the old batteries only restarts the degradation cycle again if the root cause hasn't been eliminated.

Howdy,

I am off grid with micro-hydro and solar elec. My system is 24 volts, 4, 6v, Rolls batteries. This set is into the 5th, maybe 6th year. I use a specific gravity tester to check the different cells. It is the only way to get a true reading for lead acid. I have let these batts drain down to 55%, tri metric meter. I know this is low but this is what happens whan you get used to elec. and have refridge/freezers. For the past year and a half or so I have been recharging at 80%, keeping the water levels up, distilled water only, AND I am able to run an equalizing cycle, timed higher voltage(32 volts for up to 8hrs). I do this about once a month or 6 weeks or so. This is one of the features in my Trace Charge controller(antique). There is also this feature in my Outback CC which is mainly for the solar system. Equalizing charge does boil the water in the batteries.  Tri Metric Meters up to 100% full.  Reading about equalizing sometimes it may take more than 1 cycle to get batteries up to near full charge.  The only way I can get a reading of when the battery/cell is fully charged is by the specific battery tester.  It is a baster test tube, has a red/recharge, white/fair, green/good meter, floats in test tube, draw water from cell with bulb/baster end.  When this tells me I am in the green, I then check the voltage of each battery, should all be the same.  Sometimes, electric meters say 100%,batts. full etc, and my specific gravity is still in the Fair/Mid zone, batts. not fully charged, run equalizing cycle, etc...

Is one battery lower voltage than others?  Can you pop the cell caps? Check the water level?  Specific gravity meter is an auto parts store item for a cheap one.

The original poster said they were small sealed lead acid batteries. As such they should not have a high voltage equalization charge applied to them. The water in them is finite and any overcharging will result in a little bit of it boiling away. Most times a "sealed" lead acid has a pop off top not really meant to be removed sometimes even epoxied in place that can be removed and a very little bit of distilled water added back in to give you another chance. What usually kills small sealed lead acid batteries is applying a much too high charge current to them and expecting them to take it. They should not be charged at anything more then 10 percent of their rated amperage per hour to avoid them heating up too much. A reconditioning charger will try to give them a higher voltage lower amperage jolt regularly hoping to dislodge some sulphates on the plates that can redisolve and make the acid stronger again. It may or may not work and real chargers like that are expensive. Try the water and slow charge first. A high amperage drain for very short durations can also dislodge some sulphates and Is a cheaper solution once you check the water levels and try a slow recharge.. failing that, they are dead and you recycle them and chalk it up to experience.
Cheers, David Baillie

David Baillie wrote:The original poster said they were small sealed lead acid batteries. As such they should not have a high voltage equalization charge applied to them. The water in them is finite and any overcharging will result in a little bit of it boiling away. Most times a "sealed" lead acid has a pop off top not really meant to be removed sometimes even epoxied in place that can be removed and a very little bit of distilled water added back in to give you another chance. What usually kills small sealed lead acid batteries is applying a much too high charge current to them and expecting them to take it. They should not be charged at anything more then 10 percent of their rated amperage per hour to avoid them heating up too much. A reconditioning charger will try to give them a higher voltage lower amperage jolt regularly hoping to dislodge some sulphates on the plates that can redisolve and make the acid stronger again. It may or may not work and real chargers like that are expensive. Try the water and slow charge first. A high amperage drain for very short durations can also dislodge some sulphates and Is a cheaper solution once you check the water levels and try a slow recharge.. failing that, they are dead and you recycle them and chalk it up to experience.
Cheers, David Baillie

Thanks for all the responses and I'm always loving the depth of knowledge here at Permies on issues like this.  David B., a few questions...first, I was completely unaware that SLA could be opened to add back water....I certainly may try this on the worst one if less invasive approaches don't work.  I do wonder about charging and didn't know that a 2A charge might be too high for the 10Ah rating on the battery,,?  The 12V light bulb trick to slow drain the battery I have heard of before....would one of those 12V dashboard heaters provide the "high amperage drain" that you noted for potentially dislodging some of the sulfation...or perhaps even hooking it up to an inverter and plugging it into a string of 120V/60W incandescent bulbs?  In the future, I do have a newer 'smart' charger that delivers a maximum 1A charge, then shifting to slower charging and finally 'float' charging as the batter gets fully charged.  If I can recondition these, I hope to stick with that in the future.  Thanks again, all!

John Weiland wrote:

David Baillie wrote:The original poster said they were small sealed lead acid batteries. As such they should not have a high voltage equalization charge applied to them. The water in them is finite and any overcharging will result in a little bit of it boiling away. Most times a "sealed" lead acid has a pop off top not really meant to be removed sometimes even epoxied in place that can be removed and a very little bit of distilled water added back in to give you another chance. What usually kills small sealed lead acid batteries is applying a much too high charge current to them and expecting them to take it. They should not be charged at anything more then 10 percent of their rated amperage per hour to avoid them heating up too much. A reconditioning charger will try to give them a higher voltage lower amperage jolt regularly hoping to dislodge some sulphates on the plates that can redisolve and make the acid stronger again. It may or may not work and real chargers like that are expensive. Try the water and slow charge first. A high amperage drain for very short durations can also dislodge some sulphates and Is a cheaper solution once you check the water levels and try a slow recharge.. failing that, they are dead and you recycle them and chalk it up to experience.
Cheers, David Baillie

Thanks for all the responses and I'm always loving the depth of knowledge here at Permies on issues like this.  David B., a few questions...first, I was completely unaware that SLA could be opened to add back water....I certainly may try this on the worst one if less invasive approaches don't work.  I do wonder about charging and didn't know that a 2A charge might be too high for the 10Ah rating on the battery,,?  The 12V light bulb trick to slow drain the battery I have heard of before....would one of those 12V dashboard heaters provide the "high amperage drain" that you noted for potentially dislodging some of the sulfation...or perhaps even hooking it up to an inverter and plugging it into a string of 120V/60W incandescent bulbs?  In the future, I do have a newer 'smart' charger that delivers a maximum 1A charge, then shifting to slower charging and finally 'float' charging as the batter gets fully charged.  If I can recondition these, I hope to stick with that in the future.  Thanks again, all!

The dashboard heater would work in probably 1 minute increments. The slowbDrain method was a trick for nicad batteries which develop a memory.

I have reconditioned several batteries and about to do another.. First you can buy premixed acid solution from any parts store and its right around 10 to 15 bucks.
First thing is remove battery from truck/car and make sure your wearing proper PPE for the job.. dont be complacent because if it gets in your eye your almost guaranteed to go blind. You want to get a large enough container to set the battery down into. Pull the covers and pour all the contents into that container. Now this is critical make sure you save about 1/5 of that old acid, put in seperate container and set off to the side. Mix up a gallon of regular water and baking soda and slowly pour that into the battery it will come up at your so step back. Pour some baking soda in the container to neutralize all of the remaining old acid.. pour the battery out into the container and rinse out. Do this about 5 X .Me personally I used 2 step ladders with some old wire closet shelving I had and put it between the 2 ladders, and place the battery face down and rinse it out really good. When you think youve rinsed it enough, rinse it again. Any left over baking soda will neutralize the new acid. Next pour some new acid you bought or make your own with distilled water and epsom salt. I think its 1 cup salt to gallon of water. Getting it premixed is full proof. So pour the new acid in the battery and top off with the old acid you set aside. Put the caps back on and do a trickle charge overnight if possible,  if you cant wait you can rapid boost it but stay close because it will boil over. Since the old acid is neutralized you can do with it as you will, it is no longer hazardous.  There ya have it.

I attempted the battery reconditioning strategy like that once.  The only thing accomplished was ruining a pair of pants.  My batteries were completely dead afterwards.

As mentioned in the first post, these are SEALED batteries.  Likely that more clothing will be ruined than the money you save buying new batteries.