It runs on a hot-swapable battery system. The specs say 8 hours at 100% usage and a week on standby for one battery which is pretty good since if you are carrying this into the field, you can afford to carry a few more fully charged batteries with you or just have a small generator.
An Intel E3845 has a TDP of 10W so assuming peak power is 1.5 x TDP, then this would draw 15W as 100% power usage. There are 22 of these devices so there is a total of 330W dedicated to just the CPUs. There is no GPU, SSDs take up very little power as well as RAM so we can assume that the whole thing is taking up no more than 400W at 100% usage. A Li-ion battery has an energy density of 110-160 Wh/kg so lets assume its 110 Wh/kg. To run this thing for 8 hours at 100% usage with 400W of hardware power usage, you would need a 29 kg ~ 64 lb Li-ion battery. Energy density of 160 Wh/kg would need a 20 kg ~ 44 lb battery.
Or get yourself a little 1000W generator and run the system for a week on 30 gallons of gasoline.