Dug up the ol' chemical reaction that goes on in a battery.

Take a deep breath:

remember, the battery is made up of alternating lead and lead oxide plates,
with sulfuric acid as an electrolyte.

the electrolyte contains hydrogen ions (H+) and sulphate ions (SO4--).
During discharge, H+ ions react with the lead(IV) oxide to give
lead(II)oxide and water;

	PbO2 + 2H+ + 2e-  -> PbO + H2O

the reaction takes electrons from the plate, causing a positive charge.
There is a further reaction to yield soft lead sulphate;

	PbO + SO4-- + 2H+  -> PbSO4 + H2O + 2e-

electrons are released to the electrode, producing a negative charge.

You can see how the production of H2O accounts for the lower specific
gravity in a discharged battery.

During charging the reactions are reversed;

	PbSO4 + 2e-  ->  Pb + SO4--
	PbSO4 + 2H2O  -> PbO2 + 4H+ + SO4-- + 2e-

Now the specific gravity of the electrolyte (sulfuric acid) increases.

I still can't see where EDTA would fit in.
I don't see any divalent cations...

Alistair