if you take the canopy off you will see the battery.
if you handy with a soldering iron you could cut the wires and solder them to a new battery
check the dimensions of where you want the battery to fit.
I am replacing a battery on a propel gyropter is is a 1s(3.7v) approx 160mah. you could go more or less mah without a problem to get the fit right.
if I cannot find one that will fit or it is too expensive I might bet a longer one and modify the canopy.
check hobbyking or ebay