It's "doable" to put the bigger battery for the receiver, but you won't be able to use the charger that comes with the plane. Well, not exactly. You could use it but it would take days to charge the battery. If you are going to get a bigger battery you will need to get a better aftermarket charger like the Triton 2 from Hobbico. Also, there is a little difference in the way that Ni-cads and Ni-mhs are charged so you should use a charger that is capable of charging Ni-mh's

[link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMAJ0&P=ML]Great Planes Triton 2 Charger[/link]

Ken