My Odyssey PC680 started to fail last season. Gradually lost power and took a long time to charge.
I believe it was in the car for 3 years. Not that impressed really, but It has had a tough life with some funky generator problems, running parallel ECU's and also powering IC pump etc.
For a quick fix I bought a very cheap Biltema MC battery:
It has more CCA and than the smaller PC680 but weighs the same, 7.2 Kg.
A lot cheaper too, but that doesn't matter if it has a shorter service life.
For us Scandinavians the availability is superb compared to other alternatives including OEM.
I have only used it for a week and it's performing well. Did one trackday without problems so it's a true gel battery with no leakage.
Mounting was the same as the PC680 with a small assortement of 2x4" wooden blocks.
The terminals are not optimal, but no worse than the PC680, and can use the same adapters. I simply bolt the leads directly to the terminals using some hex screws.
Can't really recommend it as before a couple of seasons, but I'll be sure to update the this post when/if I replace it in the future.
UPDATE: It only lasted 5 months before starting to fail. I got a new one on warranty but I'm not impressed. Charging voltage during use was 13.8 cold 13.3 hot. With the relocate I can't go bigger so it stays for now. If this does not work out I'll go trunk mounted Optima Red top which seems to be the norm.