I have a couple of these incredibly powerful 12V battery packs and I got thinking about how feasible it would be to MacGyver an engine starter out of them.
These things are rated on the package to deliver 30C and even higher: For a single set of 3 cells in series a 2Ah 30C cell will deliver 60A.
Consider this specimen: Monster Battery
5Ah @ 65C is 325A, and 5Ah @ 130C is 650A. The 130C max rating seems to indicate that the battery can be discharged in under half a minute.
I'm pretty sure many compact automobile engines can be started with this much current.
My thinking is I could buy a cigarette-lighter adapter, solder it to a beefy 4S battery like the one linked above, and I've got a self-contained car starter with a LOT more power than the pathetic "jump starter" products one might find in a store. With something like this, it basically could not be easier to use, and a 4S lipo won't even get overcharged. Once your car is started, leave it in there and the battery automatically gets topped off. (well 14.4V nominal voltage isn't the most ideal situation but it could be worse)