JoeH

About a month ago the alarm started randomly going off, most notably after driving in rain. I'd stick the fob in and it'd stop. Then the fob stopped locking and unlocking doors. This morning it was a slow crank when starting the engine. Next time I tried starting it it was dead. Got emergency jump, drove for 40 minutes and shut it off. Twenty minutes later and it's dead again. No juice for radio or anything. The battery is a year old.

Any ideas where to begin?

Moto_Guzzi

My rough understanding:
A battery can drain itself(Faulty from inside the battery), it can be drained by unwanted source(from outside battery), it cannot keep a charge(Inside or outside), It's not charged(Alternator or system controlling it).
Engine not running(Alternator not charging)=12.5V........OV
Engine running(Alternator charging)=12.5V.......14.5V(Or what is applicable to charging system design).

1-Get the car started again by jump if you follow the manual and feel ok doing it yourself.
2-Then test with voltmeter and see if alternator charge ok.
3-Check if something drains the battery, but 20 minutes seems pretty fast.
4-If alternator charges ok, get a good valued battery. Get battery tested to confirm.