Hey all, thread resurrection time!
I wanted to add to this since some yrs have gone by and prices and tech change.
I ended up buying a Deltran Battery Tender LiFeP04. It's a lithium iron battery. Touted as being safe and is what's used in all EV vehicles.
https://www.amazon.com/gp/aw/d/B00F9...der&th=1&psc=1
I found it on Amazon.com for $209, weighs 3.4lbs, has 460cca
I'll have it on a tender cuz I don't always drive my Z. I weighed my OEM battery at 39.2lbs. I could feel the weight loss when i took it out for a short drive. It cranked my Z up with ease right out of the box. Now time to get myself a proper mount! Ha Ha