Before dropping a wad on portable AC, you should consider a $99 Behringer MXB1002, runs off two 9V, and 18V phantom power off a third 9V battery. Sounds just as good as a UB802, and is actually more versatile. It's got 5 mic pre's, and it can be configured to have a discrete output for each preamp (two inserts, 2 main outs, and 1 pre-fader aux). Not all mics can run off 18V phantom, but many can. It's probably easier to just get dedicated portable phantom power units if your mics really need 48V. The only other battery-powered mixer I know of is a Samson Mixpad 4, costs more, does less.