did you know that lead-acid batteries can actually be charged in either polarity? it's the only battery chemistry we're aware of that allows that.
note also that yes, it is *technically* possible to reverse-charge most types of batteries, even alkalines, but this is universally a failure state and they do not have much capacity when reverse charged (and will only charge to a few hundred millivolts if that)
Lead-acid cells are actually symmetric (except for mechanical asymmetries in how commercial ones are designed)
@Felthry Huh, neat!
@Felthry It's technically possible to force a charge into almost anything if you abuse it enough.
@Terrana This is true! But in the case of batteries, it involves chemical changes. I'm not sure what the exact chemistry is that happens but I imagine you start electroplating off the magnesium from the MnO₂ in alkaline cells, with the release of oxygen gas which would probably make the battery explode come to think of it, they tend to be airtight
note that you should never reverse-charge them though. Modern commercial lead-acid batteries are designed to maximise performance when used in the intended operating mode, i.e. with the + terminal charged to a higher voltage than the - terminal.