Because until very recently I believed that no, that it was not possible.
But the last time in Congo, while I was waiting in a workshop, I saw some black people doing some very strange things with the batteries ... and in the end, after a lot of insisting ... they explained it to me.
When a battery is long discharged, or very old, etc ... it is said that it has been "sulphated". Basically, lead and sulfur salts (sulfate-de-lead) are formed which stick to the spongy plate of the negative and plug it all. Normally this battery is considered lost forever.
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