I need to have the 48V Phantom power button on when recording with the battery, correct?
Tapermark's not entirely accurate here^. That's entirely dependent upon your mics. If they need phantom, turn the switch on. If not, leave it off (and be careful not to hit said switch).
The battery you're using to power your UA5 and the phantom switch are entirely independent from each other. Phantom power's only function is to power microphones that, a. need it, and b. can handle the voltage.
For instance, my MBHOs produce no signal whatsoever without phantom power. The Nak300's in my possession (they don't belong to me) have their own batteries right in them. If I hit the phantom power switch while using them, I'll fry the mics. And my AT831's require a much lower power supply, so they'd also fry if I used phantom on them. (NOTE: when I say they'll fry, I don't mean that if you accidentally hit phantom that you've fried the mics, but if you hit it and leave it on for any significant amount of time, you can wreck 'em).
Bottom line, again, phantom is independent of the battery you use to power the UA5. It can be used to power mics that accept phantom power. The only impact it will have on your dvd batt is to reduce its operating time IF you're using phantom power for your mics (obviously). If it's a new, 9v dvd batt you can get as much as 5 hours operating time WITH the phantom switch on. I've never run it that long without switching dvd batts, though. YMMV, naturally.
Make sense? I'm kind of tired and not sure if I'm being very clear or not...