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so I got a ups with a 12v lead acid battery that was constantly on so the water inside the cells has disappeared, initially the reading voltage was 0.3v, and when I added distilled water it generally started to go up by its own to around 3v ish.

now I am charging it, and its voltage is rising but slowly, and drops Mv moderately quickly. but what is supper odd is that it's not drawing any amps, from my bench power supply.

also to mention it's not able to go past 8v for now at least.

now, what is my question, why when I am charging the lead-acid battery it doesn't draw any amps? and is it really charging without drawing any amps?

my guess would be it needs to reach a certain voltage until it really starts to charge and hold capacity.

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  • \$\begingroup\$ If the battery has been frozen when dead, plates can bend and short to eachother. You have not included measurements of the charging load voltage and charging current, but benchtop power supplies may be limited to an amp or two to begin with. \$\endgroup\$
    – K H
    Commented Sep 25, 2018 at 4:49

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During over discharge, sulphation occurred on the plates. If porous, this sulphate can be reversed by charging.

From Storage Battery Troubles under Sulphation - Over discharge

If the discharge is continued after the voltage has fallen to the voltage limits, an excessive amount of sulphate forms. It fills up the pores in the active materials, and covers up much of the active material which remains, so that it is difficult to change the sulphate back to active material. Moreover, the expansion of active material which takes place as the sulphate forms is then so great that it causes the active material to break off from the plate and drop to the bottom of the jar.

You are able to partially charge the battery, so you have changed the areas of fine sulphation back into plates of lead peroxide and spongy lead, but the integrity of the plates are damaged. The grid structure is fragile if the battery is in an uncharged state.

The cells are probably damaged with loose material. It cannot be repaired.

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If it has dried up then most likely the battery's electrodes are oxidised. Usually these are considered irreversible damage to the battery, but if you have the means you can try look up ways to revive a dead lead acid battery though they might not guarantee success.

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    \$\begingroup\$ If it's plates are a removable type, they can be removed, cleaned, and a judgement made as to whether they are still thick enough. If they are, the battery can be reassembled and the sulfuric acid replaced. Not a process to be undertaken lightly, but not impossible. \$\endgroup\$
    – K H
    Commented Sep 25, 2018 at 4:47

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