Generic battery packs...

Well, the Mobilepro 780 uses 7.2v batteries and you keep it powered straight without any circuitry whatsoever using 6 nickel metal hydride batteries at 1.2v each. If you use a 12v battery pack, then you should use a 7809 voltage regulator to charge it.

The bigger Mobilepro 880 uses 11.1v batteries and you can keep that powered with straight 12 volts. 10 NiMH cells in series with no electronics required.

I find that 10-cell 12v packs are the most flexible and practical for building a multi-power bus. Then with various voltage regulators feeding off of the 12v in parallel, you can produce regulated outputs from 3v to 9v and straight 12v. You could power a PPC, HPC, mobile phone, etc, off of it. And you can mount a white light LED array on the end and use it as a big high powered long duration flashlight as well.