reverse charging lead acid batteries

[joestue]

I am still at work in this research.

we have a dozen or so data points now over the last few years.

one example i can give you is just recently my dad let go of a napa starting battery he had for the last 6 years. i measured its capacity at about 2 amp hours (yes it still started his gmc 20 van, a chevy 350 engine, at 2 amp hours usable capacity)

it took about 250 amp hours to reverse charge it and it now has a capacity of about 20 amp hours, floats at 13.8 volts at about 80mA. i charge cycled it about 10 times in reverse polarity, acid concentration is nominal, perhaps slightly lower than it should be. its seems to be reliable at 20 amp hours capacity.


my brother acquired a GNB sealed AGM battery home from someone who acquired a lot of them for free. these are like 400$ backup standby agm batteries with a nominal capacity of 90 amp hours. it was basically open circuit with no capacity.

we cut the top off added a lot of water and reverse charged it. took about 400 amp hours to fully reverse charge it. peak capacity upon reverse charge was 69 amp hours.. a legit 60% capacity. over a dozen charge discharge cycles its capacity decreased to about 30 amp hours.

far better than zero amp hours but it is pretty typical of a trend. take a useless but mechanically intact lead acid battery and reverse charge it and use it up. its capacity will drop but you can use it.

we took a group 27 battery from my brothers boat which had decreased to relatively useless capacity, reverse charged it and put it in my mom's jeep. it had stabilized at 27 amp hour capacity reverse charged in nov 2019 when we put it in her Jeep. it will probably last at least 3 more years into 2023


of a dozen sealed agm 5 amp hour batteries which were basically open circuit aka useless.. unknown history.. we pried the tops off.. added water to each cell.. reverse charged them and got about 60% capacity out of them.

the cost is slightly lower open circuit voltage, and higher self discharge.

[DamonHD]

After the reverse charge is done, are you operating them 'backwards', or do you forward charge them again before use?

Rgds

Damon

[joestue]

permanent use as reverse charged.

[DamonHD]

OK, thanks!

Rgds

Damon

[Scruff]

Interesting.
I've heard of this before, can't remember where, as a phenomenon of poor maintenance.

I've even seen it once when a charger was mislabelled and running a polarity indiscriminate load (incandescents).

It never occurred to me to use it as a recovery method.
It sounds more practical than lads doing acid swaps or adding epsom salts.

[joestue]

The gnb agm battery had a peak capacity of 69 out of 90 amp hours reversed. It had previously been float charged for probably 6+ years and went open circuit.

After a dozen cycles it quickly dropped to 30ah.


What i think happens is when the positive plate turns into a negative plate, it shrinks in volume, pulling active material away from the grid, disconnecting it electrically from the battery.

The negative plate (which usually never has damage) turns into a positive plate with no problems.


Once the positive plate corrodes to the point the grid breaks apart, nothing can be done.

[Scruff]

Electrolysis plating the cathode would be a factor too. Reverse charge oughta reverse sulphate too.

[bigrockcandymountain]

I remember one you did awhile back that you reverse charged, just until it was rehabilitated, and then foreward charged to use it.  Is it better to just use it backward?
I have quite a few 100ah 12v deep cycles here with almost zero storage left, mostly from abuse.

I'll be giving this a try very soon.  It will save me some serious money if i can make it work like you do. 

Glad to have you back joestue. 

[joestue]

I remember one you did awhile back that you reverse charged, just until it was rehabilitated, and then foreward charged to use it.  Is it better to just use it backward?

I dont remember doing that.

[bigrockcandymountain]

Maybe it wasn't you or maybe i didn't understand what you were doing at the time.  Anyway, I'll give it a shot and just use it reverse charged. 

[Scruff]

I believe the first step is to pancake them. Stick a resistive load on them and walk away....oh sounds so wrong...

[JW]

At some point we localized a food ingredient/salt as an additive in this type of practice. Cant remember the name of it off hand.

Welcome back joestue

[Ungrounded Lightning Rod]

permanent use as reverse charged.

Reverse-charging seems to break up sulphation that can't be broken by forward charging.  So it can be used to recover batteries that were sulphated out of usefulness.

But I'd expect long-term use reversed to damage the plates.

I'd try reverse-charging for a couple cycles, then drain them to zero and forward charge them again, and see if that avoids the rapid degradation of capacity you're experiencing.

Remember to be sure they're thoroughly discharged before charging them in the opposite direction, especially on the initial desulphation polarity reversal.  In a recently heavily discharged battery, epecialy a sulphated battery, the guts of the plate may still be charged up.  If you start reverse-charging it before that gets thoroughly drained, you end up with plates that are one type in the middle and the other type on the surface, separated by the remaining sulphation and essentially shorted out and discharging through that high resistance.  As the layer breaks down the current rises, the heating increases, and the sulphation breakdown accelerates.  This can result in thermal runaway and a boiling or exploding battery.

[joestue]

I did experience thermal runaway on a handful of small 5amp hour cells.

as for the idea that reverse charging can regain sulphate, i agree

the prior battery in my truck lasted a while, then decreased to uselessness, but it still had a 1.3 S.G.
I replaced it with a handful of used 5 amp hour agms.

I dumped the acid out of the truck battery, refilled it with water, and charged it with a 1 amp battery maintainer type charger for 3 months. Then left it disconnected for a month or two (because my brother needed the battery). The acid had increased to 1.2 as indicated by a cheap plastic electrolyte measuring device.

After the agms failed I put the truck battery back in my truck and.. i think got another year out of it, i can't recall.



anyhow, i do believe that permanent reverse charging is a significant permanent potential life saving treatment, because it stops the primary problem which is that the positive plate degrades to the point the plates break apart.

[Scruff]

In terms of cell recovery, I find this method works very well.

I do the same except I automate it with solar.

It works more often than it doesn't.

[dnix71]

Posted by: JW
« on: April 04, 2021, 06:39:14 PM »
At some point we localized a food ingredient/salt as an additive in this type of practice. Cant remember the name of it off hand.

Sodium sulfite. Used to keep salads looking fresh and as a general preservative. I tried it without much success.

Batteries that went flat from disuse can usually be recharged and reused. Ones that dries out or have warped/shorted cells are scrap.

Because the common lead acid batteries are true batteries (a stack of cells) they are not repairable when one cell goes bad.

If you want true repairability then you would do like the phone company and forklift companies do and use individual 2v cells bolted together to make the working voltage. Or do as lithium pack makers do and tap each cell with a voltage limiter/balance wire. Even then heat is the killer. If you want to just guess which cells failed it usually the ones in the center of the pack because they get hotter.

[Scruff]

Epsom salt, manganese sulphate is another variant.

I dunno if it works or not...I tend to think it as a contaminant or band-aid and if it's that bad just replace the battery. 
I tend not to lose that many batteries and those I do aren't that valuable to warrant much effort. ie the 6yo car batteries and orphans.

Lead is pretty robust once the chargers are proper. Meaning keep adjusting the settings until the battery sees specific gravity 1.275 once a month and there's usually never an issue.
These 3000 cycle batteries are attractive on paper but in realistic applications, that's longer than most people's lifetime (60 years charging once a week).
I see 2 year old batteries dead by cycle >20 all the time and penny to a pound spending more on a "better battery" won't fix it.

I've 6 year old camper batteries still in their infancy on cycle count, they used to be hard-working.

[JW]

https://www.fieldlines.com/index.php/topic,149348.msg1045665.html#msg1045665

Unknown-EDTA works as I believe the sulfates are still available for use in the battery process.

[joestue]

i picked up 3x 12v 105 ah batteries from the marina boat yard, all 3 of them dead, low specific gravity like 1.1 or less.

after a few hundreds of amp hours they all recovered a 12.6 volts open circuit but had no capacity and only a little higher specific gravity.

reverse charged 1 of the 3. after something like 600 amp hours it finally dropped below 1 amp at 14 volts reverse polarity and had a "fair" specific gravity. far higher specific gravity than it did when forward polarity and less float amps at 13.8 volts.
peak reverse capacity it ever hit was about 40 amp hours. i tested several cycles, can post more data later i'm not sure i will continue testing on the other two batteries. they are likely not worth the 2$ in electricity needed to reverse them.

another battery i picked up at the same time from the boat yard was a typical deep cycle marine battery probably 90-100 ah, it charged up fine and i measured 48 amp hours at 9 amps down to 12 volts. not going to reverse charge that one.

the 27 ah capacity reversed charged battery i put in my mom's jeep in 2019 is still going fine past 3 winters. my dad was skeptical initially but when it held up the radio all night (bad ignition switch leaves the accesories on sometimes) he didn't complain about having to jump start it in the morning...