can one demote some bad Lead acid 12v battery to use as a 6v battery?

[coachgeo]

did search here and full internet search... only found on discussion and it was inconclusive.
can you take:
> two BAD 12v battery that no longer make it much or not at all over 50 percent capacity
> discharge each below 6v.....
> recharge one at a time with an old charger that has a 6v charge setting to 6v.
> wire them together as if they were 6v batts to make a 12v bank
> maybe an inexpensive or two battery 6v balancer be needed for this to work at all?
> use this new bank as a 12v power source?
> charge them as a 12v bank (solar or otherwise)?
> if so could be done with 4 of them and then wired for 24v as if it was a bank of 6v batts put together?

just trying to maximize the use of some old batts I have before disposal. Ive run them thru a battery pulse system numerous times.... they dont improve. If this would work Id use them thru the winter for some light use thru an inverter to say a 1amp at 110v furnace fan

 

[jasonhc73]

If lead-acid, probably not unless you know how to seal the package again.

If LiFePO4, yes.

 

[Substrate]

Sounds good, but sorry no. Taking a 12v lead acid battery much below 10v (unless it's like a 1-second vehicular start) damages them severely.

10.7v is generally considered "zero", so going below that is dipping your toe into the graveyard of lead. Purposely operating as a 6V battery .. nah.

The *only* time you may have seen something related to this in the past, is when a user left the lights on in his vehicle overnight and killed his battery in the morning, and his existing 12v charger simply wouldn't recognize it to even start the charge.

Instead, a 6v charger was used at first (because it could recognize a lower voltage than the 12v charger) and start to charge. Of course that won't fully recharge a 12v battery, so the user would switch to the 12v charger later.

That's probably part of where this idea may have come from. I mean do what you want, but just don't want any kids reading this carting home a bunch of dead-lead from behind the auto-parts store, and being disappointed.

 

[coachgeo]

now that thinking more this would be a good experiment when considering possiblities of survivalist living from collected junk batteries to extend an existing bank of of a good batts.

so .... what about :
>stringing bad 12v's together based on their average sad resting voltage (as long as its above 11v?) till you have a bank of batteries that are just ABOVE a desired final volt about.
> Solar charge them at desired output...
> ?maybe power draws done thru a converter to bring it to an exact desired voltage?

example.... 24v desired output
> take 3 battery that rest at 11 to 12 volts.
> add them together for a total of 33-35v resting volts
> use batter balancer ?
> charge at 24v*
> ?maybe adjustable converter? or similar to clean the 24v output.?

* would choose 3 batts trying to reach resting close to 36v then use converter to 24v...... but my solar chargers; and likely everyone else's, charger only have charge settings of 12 or 24v.... hmmm with that in mind what about

or seperate idea.. more survivalist hokey

Take three 12v batts at least each 11v

. useing existing good batts and solar system
> via inverter from the good batt bank; use an old school industrial battery charger and charge to 36v (which I have) the sad bank.
>> granted it never actually reach 36v so manually shut of charger when a volt meter placed on the sad bank shows a reading of something just above the original total resting voltage they tend to sit.
> use coverter from 36 to constant 24v (only thing I dont have).
> Not sure from here best usage of the two banks...... open to ideas here.
>? prioritize the good bank and when it gets to x? DOD level kick things over to the sad bank?
>? visa versa of above ?
>? keep sad bank in mostly unused reserve. reserve only used via buck buck type constant output converter, to charge good bank back up. This to get you by those times where sunny skies were not just plentyfull enough.

 

[Charleswgibbs]

There's more to batteries than just their resting voltage. Batteries that old/abused/damaged will likely have a severe voltage drop under any sort of load making them useless.

A little different but I remember as a child thinking I had a great idea to use old AA and AAA batteries. A fresh one is 1.5v and a dead one around 1v. So two dead ones in series should be around 2v, more than enough voltage! Unfortunately it didn't work, they were unable to put out any usable power.

 

[justgary]

If you figure this out, please let me know so I can use my 8 Group 8D batteries.

You can do what you want by finding the internal bus bars connecting each cell in the batteries. You can then drive a screw through the case and into the bus bars and find any good cells. It is then a simple matter to wire the good cells into whatever battery you need.

The problem is that all of the cells will degrade similarly in a particular battery unless one just happened to short or leak electrolyte. As just mentioned above, the internal resistance continues to rise in degraded cells. That primarily means that it is very hard to charge them and they won't source much current.

 

[12VoltInstalls]

Short answer is no - battery isn’t rated on ‘capacity’ it’s rated on the sum of cells rating

 

[Risky Rob]

Try some of the YouTube tricks to restore lead acid batteries. In a MadMax scenerio we might be salvaging batteries out of cars and cell phone towers.

 

[Hedges]

Each individual cell has to be maintained at proper voltage, both to deliver capacity and to not rapidly degrade further. Can't use a nominally 2V lead-acid cell at nominally 1V, it's chemistry doesn't support that.

Capacitors, including super-capacitors, you can run at half voltage.

What you could do, if you could access the tie bars between cells, is use the remaining good ones.
A 12V lead-acid battery is six nominally 2V cells. If a couple cells were badly sulfated but the rest were good, you could use 3 cells as a 6V battery.

I had a bad Optima and was able to locate a busbar in the middle, drilled and tapped it an connected a battery terminal. But enough cells were bad I was not able to use it as a 6V starting battery. (Optima sells a 6V half the size of their 12V but for close to the same price.)

 

[Risky Rob]

Each individual cell has to be maintained at proper voltage, both to deliver capacity and to not rapidly degrade further. Can't use a nominally 2V lead-acid cell at nominally 1V, it's chemistry doesn't support that.

Capacitors, including super-capacitors, you can run at half voltage.

What you could do, if you could access the tie bars between cells, is use the remaining good ones.
A 12V lead-acid battery is six nominally 2V cells. If a couple cells were badly sulfated but the rest were good, you could use 3 cells as a 6V battery.

I had a bad Optima and was able to locate a busbar in the middle, drilled and tapped it an connected a battery terminal. But enough cells were bad I was not able to use it as a 6V starting battery. (Optima sells a 6V half the size of their 12V but for close to the same price.)

That's interesting. Identify and link the functional cells of multiple 12V lead acid batteries to build one with enough voltage.

 

[Hedges]

Start with an equalizing charge, let settle, check SG with hygrometer (FLA). That will tell you if it's worth performing surgery.
AGM, it is possible to equalize but needs to be done more gently. Follow a vendor's instructions.

Maybe if some cells are dead others are also in bad shape? Or, with some perpetually low, the rest were getting an equalizing charge (excess voltage.) If you kept up with watering they might be OK. That could be the case if you watered religiously but neglected equalizing.

I've got some 14 year old SunXtender AGM that still function but tested to only 40% capacity at 0.15C discharge. I tried equalizing and it did pull the resting voltage up some. At higher load (one 12V battery powering 12V inverter as compared to 4s powering 48V inverter, with 600W load) it reached low-voltage warning rapidly. They aren't good for much but I'm using a 48V bank under mostly float conditions, testing inverters as part of a system.

 

[stienman]

Figure out what your time is worth, then figure out the best case scenario of battery capacity you can recover, then figure out how much you'd spend to buy that capacity in batteries that are known good and will outlast this frankenstein battery you are proposing.

I doubt the return on time investment is worth it, unless you literally have nothing better to do with your time.

For example, if it'll take you 8 hours to put together a frankenbattery with 1kWH of energy (12v @ 83AH) and you could instead work at McDonalds for $15/hr for those 8 hours, then you're spending at least $120, not including materials. That seems like an ok price for 1kwh - if it was a brand new 1kwh battery with 10 years of life and an actual usable 83AH, but that's not what you're going to end up with. And forget trying to charge/discharge it at 0.3C, nevermind 1C. You'll be lucky to draw 300w of power off it before it drops V too much, regardless of its charge level.

The tradeoff makes sense if you're in an area or position where you can't get good batteries at a reasonable cost, or your time really isn't worth much, so doing this is actually the best use of your time. If so, you will have to cut into the top and attach to individual cells. Sometimes the cells degrade evenly, sure, but that seems to be rare - more often I've found one or two cells severely damaged/degraded, and the rest just degraded. Use a capacity meter on the whole battery, and on each cell, then decide how to proceed - until you know what you're dealing with your attempts will be shots in the dark with no useable battery at the end.

 

[stienman]

And I'm saying this as someone who spent way too much time testing, sorting, and building a pack out of 15 year old LiFePO4 cells. I got 7kwh worth of battery out of cells that would have been 14kwh new, but I can't use it all due to high internal resistance, cell to cell differences, etc. So I understand trying to squeeze extra life out of bad batteries - but I'd never spend similar effort on lead acid. It's just not worth the time.

 

[Substrate]

Try some of the YouTube tricks to restore lead acid batteries. In a MadMax scenerio we might be salvaging batteries out of cars and cell phone towers.

Yeah, the reality is that things like this are promoted in the 3rd world, to make a profit by diverting the normal lead-acid waste stream, and piles of toxic lead are now all over the neighborhood.

There is a large-market for "revival" of doo-dads, books, and save-the-world going green with toxic lead to be had. Other than a single one-off goof project, there IS a marketing demographic for this. Don't be part of that sales demographic.

 

[Risky Rob]

Yeah, the reality is that things like this are promoted in the 3rd world, to make a profit by diverting the normal lead-acid waste stream, and piles of toxic lead are now all over the neighborhood.

There is a large-market for "revival" of doo-dads, books, and save-the-world going green with toxic lead to be had. Other than a single one-off goof project, there IS a marketing demographic for this. Don't be part of that sales demographic.

Why are you so sure all the YouTube techniques have no value? Opinionated people make for stupid forums. Don't be a part of that demographic.

I think it's interesting to try these tricks and report the outcome. I had luck restoring one failed starting battery. The YouTube trick was trickle charging it, then discharging it for a period of days. About 6 months later, and it still operates within normal parameters.

 

[Substrate]

Yes - keep promoting this. The toxic revivers love the attention it gets from us nerds.

It validates their existence, and then they use that to prey upon the poor.

 

[Risky Rob]

Yes - keep promoting this. The toxic revivers love the attention it gets from us nerds.

It validates their existence, and then they use that to prey upon the poor.

Stop clowning us. I personally tested this YouTube trick, and it worked.

 

[Substrate]

Hah! Look for the weasel word "trick". And that's what toxic-revivers do. They have this type of gear, and then pawn it off on the poor who know squat about batteries.

When the battery dies *again*, where do the poor put it? In their backyard.

Think like being a drug-dealer, only the drug here is lead.

P.S. Did you *ever* heed the warnings about Schumacher Speed-Chargers?

Part of the reason it works is that it does a high-voltage EQ, even though your display may only show your CV setting (or chemistry option - like flooded, agm, or gel).

And they do this on AGM! So part of the recovery process is to take a knackered agm, and hit it with 15.6v. That works. But use this on just a normal agm needing a charge? Rice-Crispies.

None of the 'tubers even know this. Nor do they use their own measuring gear on the *terminals* to witness this during charge, tracking the min/max voltages. Kills normally good agm's. However, PURE-LEAD may handle it, although not recommended unless you know what you are doing. That SBS might not go rice-crispy, but a conventional one, like a brand new Deka? OUCH.

ONE way to charge an agm with a Speedcharger, is to purposely use the wrong chemistry and set it to gel. This has caused a LOT of confusion with this one-time exception for this brand of charger - because it is about 0.6V too high when it goes into the EQ mode behind your back. A multimeter on the terminals will tell you. The display won't.

Leave the "tricks" for kids, scammers, and toxic-waste drug dealers.

 

[Substrate]

More agm overcharge fun:

Did you know that back in the day, Sears used to sell rebranded pure-lead Enersys "Platinum" agm's? And that they sold a "Platinum Charger" that looked exactly like the Sears "Gold Charger"? Speedcharger guts.

The difference is that Enersys knew that the "gold charger" was an agm battery killer, and the firmware in the platinum-charger was according to Enersys specs, and not so aggressive with the behind-your-back 15.6v eq as comes with the standard speedchargers.

Nowadays, Enersys sells their own properly-algo'd chargers to help make sure that a consumer doesn't use some random Schumacher speed-charger on good batts.

But yeah, that hidden EQ is part of the reason that your trick setup is "reviving" some old sulfated batts.

But unless you are a battery nerd and track this stuff, (with actual ownership and measuring gear on the terminals) the tubers and scammers live on!

 

[Quattrohead]

I used a knackered battery as a large capacitor/regulator for a car charger to run my CB when I was a kid.
One day I was bored and using a piece of wire to make sparks on the battery terminals.........a few seconds later one of the cell covers was embedded in my bedroom ceiling