Warm voltage regulator
Theory

Generically, 

warm = power flowing through

very warm = a lot of power flowing through

batteries provide power over time (energy)

therefore...

dead battery.

Application

Sounds like something is drawing current when your car is "not running". 

Might be a partial short somewhere, an accessory (radio, CB, entry lights, trunk mounted amplifier, etc), or failing switch/relay/linkage.