View Full Version : Old sealed lead-acid batteries: garbage or restorable?

10-31-2013, 11:51 PM
I find I need a smallish 12v battery, and remembered I had several 7ah lead-acids stashed away and forgotten. They read less than a volt. I don't recall them having problems, just that I didn't have a need and neglected them and didn't trickle them occasionally as recommended. Are they for the recycler, or can I recharge them? Info I could find was more about desulphated batteries that failed.

A new one is only $20, but "waste not, want not" is nearly the forum motto!

11-01-2013, 01:02 AM
I have a 17 Ah SLA with a date code of 1999 or something and I have occasionally left it in my tractor for a year or two outside, but it has always had enough voltage to light a small lamp. Usually SLAs are OK for at least a year with a good charge, but if they go below a few volts, they are probably good only for recycling. I have some small ones that went that low and they would not take a charge, even with as much as 20V applied through a resistor.

I have had good luck with this company:

I found some threads on another forum that may be helpful:

11-01-2013, 01:34 AM
First try to recharge them. Don't drop an ancient pos ""charger" on them, but use something modern and smart. Mine will not apply a constant charge if the battery is below 5v; it applies the current in pulses until the voltage rises above 5, then a constant current charge at about the 20hr rate (be careful with the small sealed batteries - that's about 3-400ma) until they get to 11v, then "normal" constant current charging (at the 10hr rate) to completion.

J Tiers
11-01-2013, 08:37 AM
I'd go so far as to say to keep the charge rate very low until at least 1.5 V per cell. About 9V on a 12V battery.

There isn't any real capacity down there, and it won't take that long if the battery is chargeable in the first place. Long-discharged batteries may have re-crystallized their sulfate on "electrically inaccessible" places, or it has fallen off and is lying in the bottom, in which case the battery has permanently lost capacity.

11-01-2013, 08:44 AM
Back in the early 70s one could by a product to restore a battery. It would revive a totally dead battery. That product did not make it long on the market

11-01-2013, 09:28 AM
The enemy is lead sulphate.

If you flatten a LA or SLA battery it will beging to deposit lead sulphate on the plates (Sulphation).

If you recharge the battery in a timely manor you should be able to regain the most of the original Ah capacity of the battery (as the lead sulphate will be soft).....but if you leave the battery flat,the longer the period, the more of the lead sulphate hardens. Eventually you have a battery with a good formation of hard lead sulphate ..and it time to scrap it.

A good checking routine (with monthly top ups if needed) and nice temperatures should keep an LA /SLA battery in good condition for years


11-01-2013, 12:37 PM
Thanks all. It sounds like a losing cause. I don't even have a low amp smart charger for LA, just a 2/10 amp smart car battery charger and a very smart small charger (Maha 777+)that isn't for LA, it has a switch for either NiMH or Li.

The primitiveness of battery tech is really amazing when you think about it. By far the most amps stored worldwide is in LA, a pretty ancient technology. I keep reading about R&D on stuff like nanotube batteries, but nothing yet. Remember we were promised fuel cell batteries?

J Tiers
11-01-2013, 08:12 PM
The enemy is lead sulphate.

If you flatten a LA or SLA battery it will beging to deposit lead sulphate on the plates (Sulphation).

Actually, the lead sulfate is WHAT MAKES THE BATTERY WORK. No sulfate, no battery.

When you charge a battery, you electrochemically convert the sulfate to sulfuric acid in the battery water. When the battery is discharged, all the acid has been used to form lead sulfate. YOU HAVE TO HAVE SULFATE, OR IT ISN'T A LEAD ACID BATTERY.

The TRUE problem is when the sulfate is no longer easily converted to acid..... when the electric current cannot reach it, because it has been dissolving and re-crystallizing in a form, or in a place within the cell, which is not as accessible to the electric current. The sulfate itself doesn't conduct very well, and it can be quite difficult to convert all of it to acid once the recrystallization has happened.

11-01-2013, 11:45 PM
The scrapper in my area pays 28 cents/pound. They probably won't be much good if they have been sitting dead for a while.


11-02-2013, 01:12 AM
The last lead smelter in the US is closing at year end so the may be worth more, who knows?

11-02-2013, 07:00 AM
Actually, the lead sulfate is WHAT MAKES THE BATTERY WORK. No sulfate, no battery.

And it is also the enemy ..

As on each recharging (or flattening) some of the lead sulphate will not recombine into the electrolyte, it slowly converts to a stable crystalline form that no longer dissolves and so begins the eventual death of a battery.

JST... Where in my post did I state that Lead Sulphate is not part of normal battery operation?


J Tiers
11-02-2013, 08:15 AM
JST... Where in my post did I state that Lead Sulphate is not part of normal battery operation?


Pretty much what I originally quoted, which has a definite implication that it is some undesirable effect. Since normal operation "deposits lead sulfate on the plates", it clearly isn't the "enemy" that destroys batteries, as you apparently know.

Enough folks actually BELIEVE sulfate is some sort of alien byproduct that contaminates batteries, that when I see a statement like yours, I may make a comment.

No sense contributing to ignorance, even if you yourself know better than the words you used.

11-02-2013, 09:07 AM
which has a definite implication that it is some undesirable effect. Since normal operation "deposits lead sulfate on the plates", it clearly isn't the "enemy" that destroys batteries, as you apparently know.

As it is lead sulphate in hard crystalline form that leads to degredation in LA batterys....the way the battery is used and cared for has significant implications for how long that battery will last in service. which was the essence of that post.

Cherry picking one line of my post , betrays the major portion of the text.

Had I written...

.................The enemy is hard crystalline form lead sulphate.

.................If you flatten a LA or SLA battery it will begin to deposit abnormal crystalline deposit of lead sulphate on the plates (Sulphation).

It would have technically much more accurate ,but it would not have changed the context ,the essence of the whole post.

I stand by my assertion that its the enemy , as its effects can be fought by careful handling of the battery.


11-02-2013, 11:47 AM
I had 6 golf car batteries 10 years old at the cabin. My son took some friends & forgot to turn off the inverter & it wasn't found for close to a year. I was going to scrap them all so they sat for another year. A friend bought a charger that supposedly renewed sulfated batteries. It seem to restore 2 but they didn't last long. I assume it broke up the sulfate shorting the plates but then it settled back to the bottom & shorted them out again but it fun trying. :'(

11-02-2013, 02:23 PM
How sealed is sealed? I often find SLA batteries here in the UK that have been rejected for poor performance actually just need topping up with distilled water, the rubber seals in the mechanism which is supposed to condense the evaporated water and return it to the cells fail, and the battery is no longer "sealed" if you can get into it (you may have to lever off a glued on cover, usual safety disclaimers apply, wear eye protection and NCB suit), check the cells for electrolyte level, top up if necessary, then try a charge. If there is some (any) voltage detectable, and you get a deflection of the ammeter needle they will usually charge up, and be usable, but may need trickle charging to keep them good, give it a try, what you got to lose?

J Tiers
11-02-2013, 09:17 PM
if you want to restore them, the thing that has to be done is to somehow get the inaccessible sulfate to participate in the process.

The "pulse" type chargers work (in some cases) by giving a higher voltage "jolt" to the battery. The idea is that the higher current backed by higher voltage will set up a different and stronger field (voltage) inside the cell that will pass current through some of the sulfate and get it driven back into the electrolyte (charging the cell).

It probably does work, the theory is good. Whether it can get a good percentage of the sulfate back into the electrolyte is probably dependent on what condition the cell is in.

I have restored a couple batteries by providing a high voltage through a resistor, a voltage higher than normal. These batteries were not accepting a charge well, so they went high quickly. I used unfiltered rectified AC (higher than battery voltage, but not direct from the line, in case anyone freaks out and wants to explain things to me) so there was a sort of "pulsing" to the applied voltage because of the peaks. It actually worked to a reasonable extent, I got maybe a third or maybe half the capacity back, from a condition where there wasn't much at all.

A purpose-made pulse charger should do better.

Rich Carlstedt
11-02-2013, 10:04 PM
In the old days, when batteries went dead, they sold a "recharge kit" which was sulfuric acid to increase the electrolyte ,
and supposedly you were to hit the battery with a heavy charge to flake off the sulfated portion of the plates until the battery
heated up, then you stopped to prevent the plates from warping.

I am not advocating this , only commenting on a old approach


The Artful Bodger
11-02-2013, 11:29 PM
Unfortunately you can still see in impoverished countries small children busy cutting the tops off truck batteries and rebuilding them with the best cells.