If the battery is fried due to insufficient electrolyte it can go low resistance and drag the voltage down from the Reg/Rec, charging circuit. Of course the opposite could be true in that the charging circuit has been pumping too much voltage into the battery and boiled it dry. Personally, the battery is dead so will need replacing anyway....but when the new one is fitted to the bike you need to check the charging voltage to make sure it is in the right area as suggested above. If it's too high then you run the risk of boiling the battery. I think for a 6v system you'd need to see 7 - 7.5v at the battery....any more and it'll boil the battery...any less and it just won't charge it.....