As you probably know, KWA's are all LiPo ready. However, if you plan on getting the KM4A1, the handguard has a very tight battery space, at least on the one i got. So i just sanded down the handguard and now im able to fit a mini 9.6v in it.
And with my experiences with LiPo, I love the ROF and trigger response you get from it, but they blow out really easy. Just a heads up, if you plan on a LiPo, be very careful with them. like dont overcharge or discharge it.