I have never run a total loss system, but how is this for a suggestion?:

Try running a Lithium Iron Phosphate Battery (LiFeSO4) with about twice the amp-hours of the standard battery?
OK, this is probably not a good idea if you are going to be doing long races. So not a "complete" solution I know.

Standard battery YTX4L-BS is rated at 3 amp-hours and weighs approx 2.5kg?
LiFeSO4 battery (see here for a couple of examples) is rated at 7 or 9 amp-hours and weighs approx 0.5kg

Just thinking out loud.