sorry, couldnt quite figure out which section of the forum to post this... mods feel free to move it. so... I`m a total noob when it comes to electronics so I have been doing a lot of reading and searching. to give you some background here is my situation: I installed the innovate supercharger kit on my car recently (love the kit). However, the weight of the blower makes the front end very heavy and made my rear end really twitchy. I am now looking at every single way to make the front end back to the oem weight or lighter with the kit on the car, and one of the easiest ways is to utilize a lighter battery. My friend makes a lighter battery kit for our cars using the Shorai battery kit (super awesome guy, quality product http://store.kcmachine.com/collections/lighterisbetter-battery-packages-for-subaru-cars/products/subaru-brz-battery-tray-and-shorai-battery-package-preorder), but the only issue is that I am often gone for about a week and a half on business trips and I do not have time to unhook the battery every time I go to the airport. Hell, I barely make it on the plane most of the times. The battery kit is super light and has more cranking power than the oem battery, but the capacity is too small for me. so, this lead me to the idea of relocating the battery to the trunk. I know I`m not saving much in terms of overall weight vs the lightweight battery kits in the front (heavy gauge wires running through the entire car, etc), but it`s a great chance for me to move the weight bias more towards the rear to have a similar weight distribution as the way it came from the factory. I also do not need the spare tire thanks to AAA. After looking at this thread (http://www.ft86club.com/forums/showthread.php?t=83885) I found out the specs for OEM battery is: 360 CCA 60 Ah 29.5lbs considering the fact that my OEM battery died after 50k miles and people in general have issues with the battery draining quickly on our cars, I decided that I need something that has more cranking power and capacity. Also, if the battery itself was a bit lighter, it would possibly make up for the weight of the heavy gauge wires that I would need for relocation. same weight as the OEM battery but in the rear minus the spare tire seems like an overall win win to me, especially if the battery performance is similar or better than the OEM. now, I found this chart on NASIOC (http://forums.nasioc.com/forums/showthread.php?t=1852892&) which is extremely helpful, except the list does not have CCA and Ah. I have been finding specs online for each of these batteries but have not found an ideal solution yet. Also, is it true that the battery needs to be ventilated? looks like BMW or Miata just has the battery kind of sitting in the trunk but not necessarily vented to outside... cliff note: - need a dry cell battery that is lighter than OEM but has more CCA and Ah thanks in advance.
Venting will depend on the type of battery you run. Traditional lead acid batteries require venting and need to be placed in a battery box if installed in the trunk with a vent. The batteries you see in the trunk of BMW's are AGM batteries which do not require venting. Lithium batteries also do not require venting. An AGM battery you may want to look at would be the Odyssey, similar size to the lithium but a little heavier. Many people on NASIOC have used these for years and had zero issues. Keep in mind they do not like heat so you'd need to relocate it in the trunk or under a seat to increase longevity. They do not like being kept in the engine bay. The lithium batteries like the Shorai are supposed to stay charged even when not in use, unlike traditional batteries that will die from sitting for an extended period. In theory this would be fine for you leaving your car at the airport and not shutting off the battery, BUT if you have any parasitic draw in the car it can still be killed faster than a traditional battery. I did a ton of research on these lightweight batteries for my WRX and ultimately was going to order the Shorai and mount it under the passenger seat. Unfortunately life got in the way and I haven't pulled the trigger on one yet so I can't comment on the longevity of them.
+1 on Odyssey batteries AGM batteries don't require it but BMW's AGM batteries are vented. H8 group number. Heavy as hell but I'm currently using this battery in my trunk. 1200 CCA. Left the lights on a few times overnight and the car still cranked up in the morning without a jump