The MVP is the best bang for your buck, $40 mod out there. If you're looking for another mod at that price, I'd just get a second. In fact, that's exactly what I did. Yes, you should have a back up PV, although the chances of the MVP running out of power on you are slim.
Rather then focusing on you battery as the cause of the lack of vapor, of look at your topper. I've heard great thugs about the Nautilus, but stocks heads on any clearo seem to be hit of miss. I prefer carto tanks over clearos for consistent vapor and taste. Granted, you run the chance of getting a bad carto too, but for the most part I've had great luck with them, they last longer then coils while in a tank, and the taste is great.