Battery trouble after car has been off for extended time

Your battery is draining. Check amp draw. I use 50 ma as a generic spec, that is .050 not even a tenth of an amp. If much higher, there is a problem. Check for lights left on in the vehicle, interior--trunk--under the hood. The best time to check is in the dark. It might drain back through faulty generator? Pull/replace fuses one at a time, when you pull the fuse on the problem circuit, the drain returns to normal, then you check everything on that fuse circuit. Any applicable trouble codes? In my area some of the national brand auto stores will check codes for free.