yeah of course you can use lipo batteries, just get a similar one, usualy 650mAh that might cut the weight
but never, NEVER charge a lipo while is attached to the chopper, in www.xheli.com you might find the battery upgrade for your falcon 40

xheli is so far a great website, they contacted me right away after i paid my heli (they are PST) and emailed me the tracking number
plus they use FedEx instead US post office which is great cutting down the time too