Not too digress from Grady's question, but I'm not so sure these things are the answer for what I need.
For example, I need a battery that is somewhere in the 450-550 CCA to start my Z with any authority. Sometimes this requires a minute of cranking on and off with a cold morning (no choke, static ignition timing, no accel pumps on carbs). Lots of fire up, run for 2-3 seconds, cut off and repeat until she runs. I'm just not sure one of these is up to it. I think it should be up to it, but a race weekend has a lot of start ups and shutdowns with no charging inbetween (I don't charge until about 4.5K RPM). I am not space limited, but I do want light weight.
I was looking at the Extreme Racing 22 series race battery which I'd consider marginal at 265 CCA. It weighs about 1/2 the weight of my current battery, a decent auto parts model with about 550 CCA. The Odyssey is a lot smaller, and a lot lighter, but I've a feeling she won't turn over my motor as long as I might need.
If I move up to a larger Extreme Racing Odyssey battery, like an extreme 35 or 40 series, then I'm back up to around 500 CCA but the weight is back up to around 25 lbs too, same as my larger lead acid battery. The Odyssey It is a lot smaller, but space isn't an issue for me.
It seems to me the biggest advantages of these batteries is their long term storage potential in that they don't need frequent charging. And, they have superior energy density, that is for a given amp hour output they are smaller than a lead acid battery. It would appear they last longer than a lead acid battery. But it doesn't seem that for X output they are appreciably lighter, unless I'm missing something here.