Originally Posted by SteveHall
The fact that turning it over gives a drop to 8V for the batteries - I think they are shot.
Measured where? If you have a meter connected at the batteries, then yes, it's likely them. If your meter is closer to the starter, you need to determine if the you're losing voltage at the batteries, or if it's your wiring that is dropping part of it (i.e. you still have 11-12V at the batteries while cranking, but resistance in line eats up a few volts before it gets to the starter - more pronounced when pulling current, mainly while starting.)