So it wont start if it sits for a few weeks?

 

You mean 4 years to my 2lb battery.

 

NAPA know how!

 

Yeah, I just throw my trickle charger on it and then it starts working fine again. It was never an issue if I was driving the car regularly.

 

Mine needs a jump by week 3 but after running 5 minutes seems to start like new. I think it has a draw on it when parked due to radio or alarm or something, even when alarm is not set. Light, cheap, and functional is all I require and it works for me.

Miata=riding lawnmower

 

What's considered a good minimum or safe cold cranking amp number?

Also, what about building a battery/super cap hybrid? Too much like work?

 

I think the battery/super cap hybrid ends up being heavier and more expensive than a reasonably sized Lifepo4.

As far as minimum sized battery- The good lifepo4 cells have huge discharge rates so you are mostly shopping for capacity and not cranking amps. Anything close to functional in terms of capacity will start the car if the cells are rated at 30c.

This is a good spread for small batteries from smaller to bigger:

ZIPPY Flightmax 8400mAh 4S2P 30C LiFePo4 Pack

Alien Motion Lithium Battery - LiFePo4 Lightweight Power Sports Battery

EVO2 16 Cell, Ballistic Performance Components

Alien Motion Lithium Battery - LiFePo4 Lightweight Power Sports Battery

I have the alien motion 12 cell in a car that sees some street driving. If my car wasn't parked in a heated garage I would put one of the larger batteries in.

 

I used a Deka 24 size motorcycle battery in a pure street car for a couple years. It was more than adequate at ~400cca. I drove the car every day, and the Deka would act foolish if you let it sit for a couple weeks, but a trickle charge would keep it happy.

 

For a lipo I wouldnt do less than 240 A*C or whatever those units are. Take the amp capacity and multiply by the C rating. With 252 the on the hobby battery it starts better than a stock battery.

 

I run a deka EXT12. My engine is high compression and requires lots of cranking to start. The Deka does better than my old stock battery. I did think about a LiPo but I've had a few go off on my multicopter due to crashes and wouldn't want that in a racecar with me in it.

 

Not a normal explode lipo but the safer lifepo4. The lifepo4's typically dont even have issues even with a puncture.