i use 4x 2300 powerex with a maha charger...
those 4 batts could easily do both sets of a phish gig...
but i always would have a spare set of four in my pocket...
fwiw - i have read alot about how the batts are important, but the charger is more important...
my charger is the mh-c401fs (i can use it in the car, too - for those trips to vega$ wheni had to leave, but wasnt quite ready
)
batteries = powerex aa minh 2300 mAh typical 1.2v
hth