I would do that if it were an option for me. I have a 4" downpipe running out my passenger fender and I've removed my Oem battery tray. If I had the option Id do just what you described.

 

You sir are my hero Every time I look at work you've done I am simply mesmerized Awesome job !

 

I went with a Lithium battery from Lithium Moto. It's not a pretty thing but it's amazingly strong It takes around a 6 pound battery to reliably start the car. It spins the motor over at least as well as the 1000CCA battery I had in there before. The problem is that since I have a C5 with the notorious battery drain, it'll kill the smaller battery to the point that it won't come back after sitting for a couple of days. That's a 600 dollar lesson learned. I use the regular battery to drive around and change out for the 6# one for track use. It's not any bigger than a motorcycle battery.

 

this is great feedback and not to derail this thread but would you mind expanding on this please?

have you tried keeping your car on a trickle charger between driving it?
did you try other smaller/lighter batteries and find them to not work?
which model number battery did you get?
how long have you had it and how often do you drive your car?

if it has equivalent to 1000cca that is awesome and I will get one for sure. I have been looking at this lithium iron phosphate battery which weighs 3lbs and some of the lotus elise guys have been using smaller ones. Apparently requires special charger/tender but if remotely reliable seems like could be a good option, although happy to pay more if gets me more reliability. If taking 45lbs off the nose of the car is as simple as swapping in one of these batteries, which aren't insane expensive relative to an optima or something, and avoid all the work of relocating the battery and any added weight of long/thick cables this seems like slam dunk

 

Let me respond to your questions, comments and concerns as best I can from my knowledge and experience.
1. Yes, I tried keeping the car on a battery tender/trickle charger while parked. That worked like a charm. Until the one time we forgot to do it after returning from the track with the car still in the trailer. If this battery goes down, it doens't come back.
2. I did not try smaller batteries as I called Lithium Moto and told them I had a 10.5:1 compression LS2 with a supercharger and wanted enough battery to reliably start it without compromise. He asked me about the lowest temperature I expected to try to start the car in as these batteries are particularly sensitive to ambient air temperature. I purchased the battery he suggested. I do have many smaller lithium motorcycle batteries I could have tried but wiring them up seemed like a pain and a 6 pound battery was already plenty light in my mind and saving another 2-3 pounds on a battery that might not offer enough starting power just didn't seem like the proper course of action in my mind.
3. I've had the current one 6 months now and it doesn't discharge hardly at all when not attached to the car. Remember, my C5 will kill even the 1000CCA huge battery in a week if left attached. Damned battery drain. Grrrrr..... The car gets driven on average, once a week if it's pretty on the weekends. If not, then every 2 weeks or so.
4. I'm not claiming that in any test, this dinky battery will perform at the level of the huge 1000CCA battery that we keep in the car all the time except for track outings. What I am saying is that it turns the car over at least as well if not better than the big battery when we go to start the car.
5. When we got the battery from Lithium Moto there was a circuit board that you could get to plug into it to balance the charge out. I'd highly recommend getting that if you decide to purchase this battery. Call Lithium Moto and speak with the owner there. What you have posted from Amazon seems like the best thing since sliced bread and a much better route to take than what I went with but I didn't know about the ones you found when I purchased mine. I need a light weight battery for my TT Stealth and I'll probably try the one you are looking at on Amazon for that low compression 3.0 liter V6.

Sorry to venture so far off topic but maybe this information will be useful in determining the best way to go with purchasing/relocating your battery now or in the future.

 

thanks! that is SUPER helpful. not a lot of reviews of feedback from anyone using these lithium batteries on vettes and other LS cars for whatever reason. I think using it at the track is a great idea. I'll most likely end up buying that $200 and 3lb one off amazon for track days and keep my huge/heavy optima in the car for street duty.

swap in this lithium battery and pull the passenger seat and that's almost 100lbs right there!