I have Version 4.923 of FSUIPC4 running on Prepar3d V2. If I set the battery life to 0 (infinite life) in FSUIPC4 and let the sim run with the engine off and the battery on the battery dies in about 1/2 hour. This was done using the Mooney Bravo aircraft and is repeatable (just perform the 2 steps listed). I am pretty sure this worked correctly in both V1 and FSX.
Also is there a way of recovering from a dead battery without resetting the sim?