You may want to check the system for a voltage drain. Start the vehicle and let idle for a few minutes. Turn it off and hook a jumper wire from the neg terminal to the terminal end on the cable (this will keep all systems alive when you remove the cable). Disconnect the cable form the battery and attach an amp meter inline to the battery. Remove the jumper and monitor the amps. 30ma is a good number. If you see like 1 amp there is something causing a drain. You can begin to pull fuses until the drain is gone. Be careful not to start the vehicle or turn on the head lights as this will damage your meter. Just something to try if all else fails.