Good morning guys. First post here.
Just wanted to let you know that a 121R battery fits perfectly on our Fits without a lot of modification, keeping a stock look and allowing you to keep the battery tray.
As with the other battery fitting mods you will have to do some dremelling, but fortunately you only have to cut the front part of the original bracket. The one facing the ECU can stay there without modification. Also, the battery box has to be cut to accommodate the larger battery. About 150% the size of the wimpy 151R...BTW. The specs are amazing compared to other batteries.









On a Note.
You will need either a battery strap or a universal bracket. In my case I used Duralast part #00678
You can find it under many different brands at every car part store or Walmart.




It's made of rubber and gives you a lot of mounting flexibility.
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Thanks for the tip and many photos.. A great upgrade.
Did you manage to determine the wieght difference between the OEM battery and the 121R ?

 

Depending on transmission a 2009 Fit has 62 or 64% of it's weight on the front wheels. Speaking only for myself I'm not keen on adding 11 lbs up front. Is there a problem with the OEM size battery starting the car over the life of the battery?

 

In my experience with the Fit the 151r battery has proven to be unreliable. I've had the Fit since 2019 and in that 4 year span I have had to replace the battery more times than I would have liked. (About 2 - 3 times now). Over the counter batteries made by Johnson controls from Autozone to Walmart.. usually have a 3 year life span.. 4 if you are lucky and live in cooler climate.

Luckily I have other cars to drive.. if the Fit were my only car I would have to call someone for help to get another battery or be left stranded.. Luckily for me the times my Fit battery has been dead is when I'm home with tools to recharge the battery and not somewhere remote.

I have to keep a battery tender on the Fit.. If I leave the battery connected on the Fit and do not drive it for more than a week it will be dead. That has happened so many times.

I like the idea of the 121r being an option.. however I do not like hacking up the factory battery tray to shoe horn it in.

 

Whatever you did to the positive battery terminal doesn't give me a lot of confidence. Are you using wire nuts? The dead battery issues you are having might be self inflicted based on some of the things my little eye spies here.

 

Lol... Man's gotta keen eye.

 

It's a curse!

 

I have a 2010 bone stock 71k miles and the battery absolutely sucks, I think it's strictly a capacity issue. we bought ours 3 years ago from a grandma who drove it to and from church, 31k miles over 7 years, I've since replaced the alternator, and the battery twice. the battery has died a number of times for various reasons like the kids messing with the dome light, but where it becomes unacceptable it it dying from turning the car off for 7mins in the pickup line with the headlights on.

So the battery died today again and I'm at a point where I just want to never have this issue again. I use a Li-Po battery in my MR-2 mostly because it cuts weight and I track it but you have to leave it plugged in if you're not going to drive it for a week and we do alot of traveling. With the Fit an extra 10lbs over the front of the wheels will probably help in the snow to get going, but you are right about it causing more front end dipping under heavy braking in emergency situations so that is a valid concern I think if I go this route I'll toss a 20lb free weight in with the spare tire to offset it.

As for this write up I think it's pretty good, parts list is always helpful and before/after pictures make it solid, there's probably 10 good ways to do this and this is certainly one of them.

 

You can go the 51R route easily. There are many threads on here. And don't worry, you don't have to put more weight in the back... Just replace the battery with a slightly bigger one and you'll be fine.