The AXIOM Beta developer kits ship with 5V DC power supply.
AXIOM Beta takes two 5V inputs (1x Microzed, 1x rest of electronics) and together draws 4A max, power consumption depends on operation and is in the 10-20 W range typically.
Two 5V 2.5A output converters should be suitable.
With batteries it is a convenient feature being able to:
Dimensions: 70 x 38.5 x Depth mm (depth varies with capacity)
Voltage: 7.2 - 7.4V
Capacity: 2600 - 6600mAh
Doesn' t exist yet but if we ever go to create one this chip might come in handy: http://www.ti.com/product/bq34z100