If I let my Cherokee sit for 30 minutes or so, the voltage gauge registers extremely low voltage, although the battery is still putting out 12 volts. If you try to start it, the fuel pump engages, but the starter doesn't crank. If I connect a charger to the battery, the volt gauge registers 12 volts and the engine will start as normal. Turn it off, disconnect the charger, and it'll start like normal. Wait 30 minutes, and we're back to not starting. Any thoughts?

 

Probably bad battery. Charge it overnight and have it load tested at a parts store.

 

Start by charging the batter and have a load test done. Just because it has 12v it can be not enough amps. If the battery checks out you need to start checking all the ground. That is were I would start.

 

When I disconnect the battery and then leave it, it starts just fine, so I'm thinking maybe I've got a short somewhere, but I'm going to take it in this week and get the battery load-tested and rule that out first. Thanks!