maybe lipo but in the down under i dont know availability or price.kokam or thunderpower in the 2000 mah range should still weigh less than your current pack.2s for 7.4v 3s for 11.1v.look for other forums containing li-polly info,or maybe some nimh.lipo`s are pricy at first but pay off in the long run when used properly.lipo`s have stringent guidelines that must be followed but when you get it down you wont be let down.nihm batteries cost less and are more durable and forgiving than lipo with nicad being the toughests but heavy.good luck