Lead battery 6v not charging, what is the reason?

Question

Batteries

Lead battery
6v 4ah
Charger Voltcraft alc8500
The battery was forgotten for two years. There was no electrolyte left. Now, out of curiosity, it is flooded with distilled water, it stood for a couple of weeks so that the salts “dissolve” a little and ...
When you try to charge, with or without an activator, the voltage in the battery rises to the nominal voltage in 3-4 minutes and then jumps twice (11 -12v) and the charger goes into protection. Gives an overvoltage error.
For what reason could this be?
Can this be fixed?
(everything that happens is for the sake of curiosity and experiment, and not the struggle for a penny battery.)

Answer 1

To do this, you need to understand chemistry. Lead sulfate is formed on the plates , which is essentially a dielectric and insoluble in water - the area of ​​​​the plates decreases.
<there is a lot of chemical theory on reduction reactions>
You can try charging with a pulsed current, causing the water to decompose. And in fact, you need a new electrolyte.