97 F150 XLT with 5.4 L triton. New battery installed in sept. 2010. engine started and ran fine. Truck sat over winter with battery hooked up. In april attempted to start engine. Battery was dead. took battery in and found battery was faulty( battery exploded upon testing). Repleced battery with new one. Light and engine check worked fine. Once key is turned to start engine a loud click is heard and then no power to any systems. Unhook battery and put on charger, battery has full charge. hook battery up and have power to vehicle (lights, radio, engine check works fine). Try to start, loud click heard, and dead again. Only way to get power back to vehicle is to unhook battery and power with charger. Any suggestions on what could be wrong would be greatly appreciated.

 

A few things you need to know.
Never store long term with the battery connected because the computer takes power at all times even though it's a small amount.
A rodent chews wire and starts a fire etc.
Sounds like the starter may be locked up.
Start relay may be faulty.
Battery cables/grounds may have an issue when large current are attempted to be drawn that low drain won't show an issue with.
The battery exploding makes me think it was discharged over time and went into a reverse condition during your storage. This kills a battery everytime.
When they put power to it it looked like a dead short and blew.
Good luck.