Love the avatar, squarehead!
Put a meter across your battery terminals (set it to VOLTS not AMPS, otherwise you'll nuke the meter and burn your hands on its cables), you should be getting at least 12 volts without the engine running. For every 2 volts you're down, that's probably a knackered cell (pop off the cell caps and look for buckled plates).
Dead cells are likely to be doubly bad because if, for example, you've got two cells that are effectively short-circuited, you're charging an 8 volt battery from a charging circuit meant for 12 volts, and the cells won't like that at all. If the battery explodes, you won't like it either.