Little Spinner ran a 37V 3.3Ah LiPo at its last event. That in its self is big enough to run some heavyweights also. It does seem a little daft that a feather weight has no limit on the size of LiPo pack but a heavy cannot run any. Maybe a pack capacity limit is needed or sooner or later someone will have a featherweight with a 20Ah 10 cell pack in it.