[Wavytone]

Epsom salts and lead alone do not a battery make.

A salt electrolyte requires alternating plates of two dissimilar metals well apart in the galvanic series (ie anodic potential) to function - copper or zinc often being the other.

What you suggest also sounds very messy, environmentally very unfriendly and potentially a safety hazard - wet cell batteries can overheat, boil or worse explode or start a fire and you don’t want to be anywhere near when that happens. Fire involving an aggressive electrolyte and electricity can get very nasty.

There is however a much easier, cheaper and safer solution - head to any auto electrical place and you can pick up old car batteries for nothing. These can be reconditioned with Epsom salts, well enough to do what you want.