How to drain to empty, NiCad camera batteries.

"What would happen if it put them in some salty or slightly vinegar, water for half an hour before recharging them?"

You would have rusty, dead batteries.

The simplest solution is to purchase a charger that drains the batteries for you, before it recharges them. It's called conditioning, I think.

Otherwise, find some device that the batteries fit, flashlight etc. and drain them using that device before charging them.

It is very important to fully cycle your batteries every time you recharge them.

Look up NiCad memory.

More importantly.... don't discharge them as a set of series connected cells, because one will always become reverse biased.

Discharge them as individual cells and then immediately recharge them.

Actually, that happened to me once. One of the batteries "reversed" according to my very basic test meter. I certainly didn't understand that - does it have a name ? If I use a flashlight with all four in at once, doesn't that mean they're in "series". I don't have anything that just works on one at a time. What can I improvise ? (besides the salty water ?) Thanks.