Hello all,
I just wanted to post my recent experience to make life a little easier for anyone who wants to install an optima battery. Hopefully this is useful to someone.
I bought an "Optima Batteries 8025-160 25 RedTop Starting Battery." It fits and works fine, except for one minor annoyance. Some batteries have the terminals towards the back (on the top) and some (like the Optima) have the terminals towards the front. For the one I purchase, this meant I had to pull the cables a little farther to reach the terminals---no big deal, but the battery would actually fit better if it were put in backwards--then the terminals would be in the back, closer to the cables. However, then the + and - would be reversed. Thus the purpose of this post: Optima makes some "reversed" "R" batteries, where the terminals are the opposite of their normal position; this is probably what you'd want to buy.
So, get the reversed terminals and install the battery backwards. Again, mine works and there's nothing wrong with it, the cables just have to reach a little further. Also, despite that the terminal posts are farther forward, you can still access them through the plastic cover/battery flap.
After reading through several posts, I found that the stock battery size is a group 48. This type of battery (stock) has dimensions of 11-3/8 x 6-7/8 x 7-1/5. The Optima I purchased has dimensions of 10 5/16" x 6 13/16" x 7 5/8" tall. Despite being a tad bit taller than stock, it fits fine. The depth is also ok, despite the 0.0625" difference.
Conclusion: if you're looking to buy an Optima battery, buy a reversed version, install the battery "backwards," and as long as the depth is about 6 7/8, the OEM mount will hold it securely. Judging from my experience, the Optima Batteries 8003-151 34R RedTop Starting Battery looks like it would probably be the best fit. Perhaps someone that has one could confirm.
Hope this is helpful!

 

Just want to thank for the info posted.
The 8003-151 34R Red Top fits perfectly in my 2008 R56S. It threw a cell (P0030) right after the installation, but went away after 2 weeks. I guess the firmware readjusted itself.

 

I thought the info would come in handy to someone sooner or later, glad it helped! I'm happy to hear the one I suggested fit. If I ever need to replace mine I will get the 34R too. Thanks for confirming the fit!

 

Thanks for the info.

Might want to add it :

https://www.northamericanmotoring.co...ment-help.html