Polarity

When the T first arrived, I put it on a battery charger and left it overnight.  The next day, the starter turned over weakly.  I was really excited by this, because that meant at least the wiring worked!  Soon after, it quit turning, so I put the charger on again.  This time, I could hear the charger clipping.   When I felt the cables they were hot.  I checked everything, thinking I had a short to ground, but everything looked OK.  Took the battery to a local auto supply store.  They put it on a tester - result; the polarity on the battery had gotten reversed.  Negative was positive, and vice versa.  If you looked at the battery, there was a very slight hump in the top of the case.  Only thing we could think of was 1) I messed up hooking up the charger, likely 2) or the battery froze after having sat so long in CA, then in the sub zero trip here, more likely.  Anyway, I am out a new 6v battery the prior owner had purchased.   Now that the slate is clean, I am considering converting to 12v, so that I can run coils without magneto.  I am sure that will warrant comments from T purists.  We shall see - still vacilating on that one.