[Rob Thompson]

There a few great threads on here about upgrading the battery on Elements to higher capacity:

Battery Size Guide 51R < 56 < 47 < 35 < 34R...

I wanted to share my accumulated knowledge after many(!) hours of research including reading every battery thread on the forums. The stock 51R is woefully underpowered for the Element, particularly with cold weather and/or any kind of electrical mod or add-on. Judging from the numerous...

www.elementownersclub.com

I just put in a 24F battery

I know there's a lot of "which battery should I put into my Honda Element" threads here but mine is going to be brief. I replaced the beyond-lame stock battery with a size 35 about 4 1/2 years ago, so the necessary modifications to the battery tray had already been done. The difference in...

www.elementownersclub.com

I just replaced the stock 51R with the huge 24F with great success. This is almost a no-brainer swap, and no real additional work needed to do it. It is a tight fit, but not difficult to get in place. Anything larger would not fit. The upgraded battery is similar cost to the factory one too. I'm just recording my notes here for others who may want to do the same.

You will need a new battery strap that fits, and longer J bolts, but our auto parts store had those in-stock too. The only thing you need to do besides removing the plastic trays is to bend the metal on the bottom of the battery plate out a little bit, because the 24F fits almost exactly into the holder, leaving no room to loop the "J" into the hole. I've added some pictures here too:

 

[Rob Thompson]

Thanks @centerpunch, great tips! I was a little worried about the rubber strap too. Maybe I'll find something like your nice fiberglass bar to make sure it is secure.