Can't open/refill lead acid battery

[Ontheronix]

Hi all,

I have bought a lead acid battery 'as new' a few months ago.
I've stored it a few months at 12,45V. Then I did some tests and discharged it 3-4 times to 12,3-12,4. (At that time not knowing that a deep discharge damages a lead acid).
A week ago, I charged it up to 12,75V to test how the condition of it was. It could power 100W of halogen bulbs for 30min. After 30mins, the voltage stabilised at 12,5V, what means it had been discharged to about 80% if I'm correct.

It's a 70Ah battery,  so I thought that 12,75V maybe didn't equal a 100% charge, and did a new charge, it took half a day to get the 12,5V to 12.8V.
I do charging with a DC-DC converter connected to an ATX power supply, at 13,8V-14V, since I don't own a dedicated controller. (I disconnect reguraly to measure the voltage (after letting it settle down) to know how much it is charged.)

So the battery sat there in my shed, fully loaded, waiting for a new test. A few days later, I measure the voltage because it had been cold outside (-2°C) and was wandering what had happened with the charge during those days.
To my astonishment I measured 10,5V! Until today I have not a clue what happened.. The battery has just sat there, not connected to anything!
I tried to recharge for 3 days, but the (settled down) voltage doesn't get any higher then 10,78V!
I also hear the battery fluid crackling and dripping, like gas is emitting, condensing, and falling back into the fluid.

I tried to find refill valves, but the housing doesn't allow any opening up.. Everything is melted together.

If someone see's a connection in all this strange story, please enlighten me
Or if someone knows how to open it, I am be curious if a refill would be needed..

It's a Honda 31500-SP0-011-HE, following are some pictures from my attempts to open it up:


Other side:


Upside:

[Crispy]

That is a maintenance free battery for a Honda Prelude. I assume "as new" means slightly used and that it could have possibly been sitting idle for who knows how long. It may have already begun to sulfate when you purchased it and if you did deep discharge it 80% 3 or 4 times that was likely the last nail in it's coffin.

The plates in car batteries are much thinner than deep cycle batteries and are easily warped at the high temps generated by the prolonged charging after a deep discharge. It also sounds like the electrolyte was boiled off so you probably have a couple warped plates that have shorted.

Used batteries are a big gamble as you never know what you are getting. For small loads like you have, a couple of 6v golf cart batteries hooked in series for 12v are your best bet. Remember to take your dead one along to save on the core charge.

If your budget allows, a cheap charge controller and battery meter will take a lot of the guesswork out and make things easier for you and help prevent accidental damage from overcharging or discharging.

[Flux]

It's lost a cell. 5/6 x 12.6 = 10.5 so you have a fully charged 10v battery that has lost a cell.

Probably it was at end of life.  Voltages don't mean as much as some seem to think.  At 12.45 it wasn't fully charged and may have started to sulphate.  Your 3 discharges to 12.4 volts shouldn't have been a disaster.

What you don't say is what voltage you got it to on charge, I assume the 12.6 was on standing, it probably went up to the power supply voltage when on charge, A few hours gassing at over 14v may not have helped things but on the other hand it wouldn't normally have been a disaster. It seems to have shorted a cell so it is unlikely that it is boiled dry and even if you can find a way to add water I can't see that helping. My suspicion is that it was taken off a car because it was failing to perform.

Flux

[Ontheronix]

I went along with the shorted cell theory, appearantly the battery is indeed charged, and just has a lower voltage!
Flux, thinking I had a 12V battery, I charged it with 14.3V. Way to much for this 10.5V battery but I suspect it has done a lot of desulfation... which is good: I tested it, and this time, a 100W load got it  from 10,75 to 10.6 in 50mins! Capacity seems to have gone up even though I now ahve 1 cel less!