So after way too much research and back and forth, I finally installed a much larger battery in our HRV.
As I detailed above, there is no perfect solution for a larger battery in the HRV.
Here is a comparison of 3 flooded lead acid batteries:
51R --- 9.5L x
5.0W x 8.75H --- 500CCA --- 28lbs --- C$109. --- Costco 4yr warr
56R ---10L x
6W x 8.3H -------- 590CCA --- 34lbs --- C$180. --- Interstate 2yr warr
124R --10.3L x
7W x 8.5H ------ 700CCA --- 40lbs --- C$124. --- Costco 4yr warr.
For most everyone, I would recommend the 56R just like Slowfosho did. 590CCA and it's a virtual drop in.
The original upper hold down bracket works, just flatten the small tab and original J-hooks are fine.
You will have to remove the plastic tray and trim off the sides so the 56R will drop in. Done.
I'm stubborn and we use our HRV for skiing all winter and after I discovered that the HRV charges the battery at low levels at times, a much larger battery was my choice.
Details on the HRV charging strategy in this thread:
HR-V Battery Problem
IMO, the small 51R battery and with the variable charging voltage of the HRV combines to cause the HRV battery issues. So installing another 51R battery is not a permanent solution.
Our 2006 Acura TSX came with a 51R battery and it lasted a long time with no issues. When it failed I installed a larger Group 75 700CCA battery when it failed 3 or 4 years ago.
To install a battery wider than 6.0" inches you will have to do some mods.
It is possible but not easy to reverse the mods. You would have to purchase or re-mod the battery metal shelf.
It's not a common Honda part and not cheap.
1. The forward ECM support bracket bolts to a tab on the metal battery shelf. You will have to cut the tab off the battery shelf, move the ECM towards the headlight and then fab up a new support bracket.
It took me a while to fab up a "Z" shaped bracket, attached and screwed to the relay box bracket.
This gets the ECM secure, out of the way and now independent of the battery shelf bracket.
2. You will need a longer upper battery hold down bracket. The original one is too short. It needs to be 7.0inches ctr to ctr between the bolt holes. I found a random one at our local autowrecker, cleaned it up and painted it.
3. You will need 1 longer J bolt, about an inch longer than the originals. Available everywhere or pick up a good used one.
4. Once the battery and plastic tray are removed, 4 more bolts and the metal battery shelf comes out.
It has metal guides on both sides that are 6.0 inches apart. Too narrow for a larger battery.
I flattened out the guide nearest the headlite. Welded on an L-shaped support, numerous test fits, cleaned it up and painted it. Plus cut the sides off the original plastic battery tray.
5. Drill a hole in the metal crossmember for the new longer J-hook to fit. Clean and paint the new hole.
All this took me longer than I care to admit. About 4 hours. Of course, I could now complete it in an hour.
5 days later and all is fine. The 124R battery is 12lbs more than the original 51R right at the front but you can't tell.
Plus I have already removed the air intake resonator and ex resonator to compensate for the extra weight!
The new battery is rock solid. Never below 12.4V every morning now. No worries, no doubts now.
The goal was to eliminate any HRV battery issues for a long time.
The 124R battery is common and available anywhere. One application if researching online is a 2012 Hyundai Veracruz.
After the mods, the procedure to replace the 124R battery is exactly the same as replacing the OEM 51R battery.
I'm not much for taking pics in the middle of a project. I should have taken pics of the modified battery shelf.
The battery is much larger but it looks OEM in the engine bay. It would take a trained eye to notice the difference.
It's solid and doesn't move, tight but doesn't touch anything. The ECM is closer to the headlight.
Again, I would recommend the 56R battery for most people instead!
1 pic shows grease on the battery terminals and J-hooks for corrosion resistance.
Weird lighting in my shop. I'm a much better mechanic than photographer!