A friend of mine has a ‘01 Montana, that keeps killing the battery. I put a multimeter to the battery, and it had 5 volts. This is the third battery this has happened to (low voltage I mean). Might this be an indicator that the alternator is bad?

If it is, is there a way to verify that it is indeed the alternator that’s bad? What other culprits might there be?

Thanks in advance!