I have been given a dead Optima BlueTop SLA battery that arrived from the USA in a caravan. It has been in a discharged state for an unknown period of time. Voltage was around 5 or 6 volts when I got it.


I have decided to try to resuscitate this battery by means of different charging techniques. I don't care if I destroy it since it is already dead and I got it for free. I just want to see if I can bring it back to life at all. If I could get it charged again, I would use it as a UPS battery, nothing demanding, just a couple amps load at most when the power is out. It doesn't have to be able to start any engines.


I am aware of the dangers of overcharging and I am working in a ventilated environment in an old garage and I am keeping close tabs on things so safety should not be an issue. I am also careful when connecting and disconnecting from the mains. I believe I have these things covered.


I am not equipped or prepared to physically disassemble the battery and play around with the electrolyte. If I can't fix it by charging, I will give up. My question is just if anyone has any tips or suggestions for attempting to kick it back into life by charging.


I have two chargers. One is an old-fashioned pre-electronic unregulated charger that just pumps out a constant current to the battery. The advantage of it is that it doesn't care what the battery voltage is. The other charger is an inexpensive 'smart' maintenance charger from Aliexpress. It has a multicoloured LED to indicate the charging state. The current output is modest and ceases when the battery is charged.


I tried putting the battery on the brute force charger initially. At first nothing happened at all, but after a few hours the battery began accepting a charge. Current flow was about 2.8 amps according to the meter and I could hear the transformer happily humming away. I left it overnight.


By the next morning the battery had charged to about nine volts. I put the small maintenance charger on it and left it for a day. The LED indicated the charging current was cycling on and off as it is supposed to but the battery voltage did not increase. After a day I put it back on the bigger charger and let it run for another day. This time the battery eventually got hot and started sizzling. I immediately cut the power. The charge on the battery had increased to 11 volts.


After the battery cooled down, I put it back on the maintenance charger. I tested it first with a 60 watt headlight, though, and that lit up brightly, though I didn't leave it on for long. So the battery is holding at least some charge.


The battery has been back on the maintenance charger for a day now but the charge has not increased past 11 volts. I read somewhere that if I leave it on maintenance charger for a week or so, there is a possibility that the low current can dissolve the sulfation and restore the battery. That is my current plan. The battery is not warm and the maintenance charger appears to be operating normally, though the battery never seems to reach full charge. I check it a couple times a day. 


If, after a week, there is no improvement, I intend to discharge the battery completely with the light, and do the whole thing over again. After that I will probably give up. Can anyone think of anything else I might try that does not involve disassembling the battery?