Yeah the weight saving is great. Both my beetles use 3s 850mAh packs, which I get from Robot Birds for £9 each. I have four packs which cost £36, can't argue with that price. One pack lasts Flatulence an entire event and more, and Spin Cycle needs a fresh pack for each battle :P
Even chargers are a lot cheaper these days than when I started, making a battery setup for a beetle nice and low-cost.