Poking a cadaver might seem gross at first, yet valuable as a study
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/grin.gif)
From the last check, the 3rd and the 4th elements appeared to be in reasonable shape, one was capable of about 3 Amps short-circuit current, the other, 7A. Both were way under the expected voltage, at only about 1.9V with no load.
Yesterday they were refilled again with water, then plugged them to charge for about 24h at 0.5A. Not the best idea, because during charging the electrolyte overflowed a little. Should have replenished the water after charging them, not before. Paper towels helped to not make a mess out of this.
Now, 24h later, elements 3 and 4 are about the same voltage, 2.0V each when left with no load, but when short-circuited the max current is still slightly different, 10A and 13A. The difference in max current is not so big now, maybe the previous 3A vs 7A was because they were not charged enough. Will keep charge them till tomorrow.
However, until now more than 20Ah were poured in each element (the battery is only 9Ah), so by now they should be fully charged, yet the voltage is only 2.0V instead of the expected 2.4V of a fully charged element at room temperature.
At this point I suspect there was so much sulfation that a big percentage of the initial H
2SO
4 in the electrolyte was fixed in the PbSO
4 crystals, so now the electrolyte does not have enough H
2SO
4 left, and that is why the open circuit voltage can not go bigger than 2V no matter how much those elements are charged.
Should either add some sulfuric acid (which I don't have any), or maybe find a way to break the PbSO
4 crystals stored on the plate as sulfation, and make them dissolve in the existing electrolyte. Normal charging can not break large PbSO
4 crystals. Will see about that later.
Even so, with only 2V, there should still be about the same energy stored as it would be stored by a 2.4V element, just that the max current will be lower. Didn't measured the C yet, so for now this is just speculation.
Not sure for how long this screws in the pic will last, but if the location is just right, self driven screws on an initial 1mm drilled hole right above the interconnection bridges can make great terminals to temporarily access each element.
![Bullshit Detector :bullshit:](https://www.eevblog.com/forum/Smileys/default/BullshitDetector.gif)