I hate carrying multiple batts around. They always need changing at the wrong time and eventually, I run out. Not to mention the high initial and replacement cost.
So, I went back to my old 2 piece video camera/recorder days and revived an inexpensive solution that worked like a charm. With the comparatively small power requirements of the HV20/30, it works even better. Here 'tis:
Picked up a 75 watt mini 12VDC to 110VAC power inverter, not much larger than a cigarette lighter adaptor from Surplus Computers for $10.
Picked up a 12V Werker 7.5 Amp Hour sealed battery (from BatteriesPlus, abt $30.
Stuffed it all in a small carry bag, added a cigarette lighter receptacle (WalMart Auto Dept. $4) wired it to the battery. Plugged in the fuse-protected inverter. Then plugged in the HV30's standard AC charger/adaptor.
Presto! Can shoot for hours on end. No worries about extra batteries, overcurrent, undercurrent, etc.
Recharge the battery with a 12VDC trickle/float charger from Harbor Freight ($10) at night and shoot all day again, tomorrow. Using this smart type charger, you can recharge the battery many, many...many times.
BONUS: Hang the carry bag low enough between the tripod legs and the 5.8 lb. battery serves as great ballast. Wanna' go mobile? Use a fanny pack instead of the carry bag.
Total Cost for virtually unlimited shooting: Abt. $60.
Just FYI. Hope it helps.