lithium ion car and motorcycle batteries

I was looking at lithium ion batteries, as a friend of mine has a harley davidson softail. He ordered one of these. It was about $200, so its not cheap, but had 525 cold cranking amps, and is 2Lbs.

I looked into the car sized ones they are around 12Lbs, super expensive, and have around 1200 cold cranking amps.

For you electrical savvy guys, forgive my ignorance, but couldent you just use the 2Lb lithium ion motorcycle battery in your car, if it delivers the kind of advertised cranking amperage that it does ?

I was thinking, if the little 2LB motorcycle lithium ion battery can do the job of a regular sized lead acid one, i would make a dummy battery out of a hollowed out lead acid battery case, and i could put the cycle battery inside hiding it along with the relays for my headlights and electric fan. Keeping a stock appearance and shedding close to 25 LBs off the front end.

Any thoughts on this?
Matt