If you want to blow your wad on some innovative battery ideas, take a look at Anti Gravity Batteries. (
LITHIUM BATTERIES, MICRO'-'STARTS – Antigravity Batteries)
As a LiFePo4 battery, it's about $850 bucks, but it has a 15% reserve that can be unlocked via remote so your whip always starts, even when you drain it down flat.
No, I don't have one of these, but it's a neat idea if you have a need.