No Power

Make sure the battery is really dead by testing with a volt meter at the battery posts themselves, scratch through the lead oxide on the battery post top as it is generally non conductive. If the battery is low volts remove both connections and CLEAN the connectors and posts with light sandpaper or whatever you have on hand (rock, pocket knife, etc) lead oxide is not a conductor you want shiny terminals. Then place on battery charger for a few hours, remove charger, check volts hoping for around 12.2 or better in engine off state. Jump starting and allowing the alternator to recharge the battery is possible but places unnecessary stress on the alternator to charge the dead battery and can kill the alternator, trickle charger is preferred but not always available. If you have to go this way shut off all the electrical accessories you can while recharging the battery.

The battery has 6 cells in series of 2.1v each at full charge or 12.6v total. If one cell shorts through or fails it will check 10-10.5v after charging. If any of the internal connections between the cells mechanically fails the battery will check 0v suddenly and this can be intermittent if it is moving around inside.

Dirty terminals or loose ground can keep a good battery from getting charged by the alternator normally. The alternator can usually support vehicle operation while running with a poorly connected battery concealing the problem. The result is a dead battery immediately after engine off.

Bad alternator can keep a good battery from charging, when running the voltage should check 13.0-14v at battery terminals or more, my digital meter floats between 13.7 and 14.1 while driving. Again check voltage on top of the lead post for levels at the battery, not on the connectors.

Bad alternator or belt slip or belt failure usually illuminates the battery light on the dash a few minutes before the engine dies. If you see this light while driving you have little time left before being stranded, been there in a 08 Grand Cherokee, had maybe 10 minutes of operation left when alternator failed.