Honda Fit Battery Swap – 151R to 51R

Noticed very recently the battery for the Fit was feeling pretty weak – start ups were taking a bit longer than usual. The dash lights would flicker during start up. The windows would make noises like they were struggling. The effects were exacerbated the colder it was or the longer it sat, and twice to my disbelief the battery was dead and had to be jumped. Hopping online, I quickly found out the stock 151R battery was notoriously bad, and given that this car is a 2010, the battery had outlasted most stock batteries (unless my sister has previously changed it). Looking online, it became clear the solution was to go from a 151R to a 51R. Moderately larger in size, particularly length, but packs 500CCA compared to the stock 330. I looked through a few posts and decided this was a doable modification for me.

Requires:

  • 51R battery
  • 10mm wrench
  • Dremel (for cutting/grinding)
  • Basic tools

This DOES require cutting/trimming with a dremel, but this was the solution I found most reasonable. Please do at your own risk. If you feel uncomfortable, just take it to a professional.

Old battery at the top – new battery at the bottom. Went with a 51R from Advanced Auto because of a coupon I had. I believe any 51R is equivalent. The Autocraft Gold came with a 3yr warranty.

Old battery removed

Test fitting the new battery. It was a squeeze – but don’t be discouraged, it fits! And I think the 51R I got was a little longer than other 51Rs. Note, I took off the blue clamp that was holding the main power cord that leads to the red terminal in this picture. Fairly typical plastic clip, I just wedged in a screwdriver and knife on the sides to undo it.

There was also a 10mm bolt holding the other side of the terminal, as shown in the picture. Undid that bolt so I would have more room to move it around.

I cut the corners of the right side of the battery holder so I could still use it – I didn’t cut the right side off though, just the edges, so when I sat it down it would still be of use.

Most importantly, which I neglected to take a picture of – I dremeled down the right side of the airbox. The airbox had a lot of fins that needed to be dremeled down so the power cord could slot between the box and the battery, so it sits as it does shown in the picture. Also reinstalled the battery tie down.

Last thing I cut off with the dremel. Maybe my particular battery was a little tall, but there were plastic edges on the right side of the full power terminal that stuck down like two stalactites – they were preventing me from sitting the connector down as much as I wanted to. I struggled trying to get it on without doing this, including using aluminum foil to make the terminal a bigger surface to clamp down on. It still wasn’t good enough, so I did have to cut those down to get it where I wanted.

Overall, I’m extremely happy with this modification. The car starts up so much quicker, and I feel like the battery is going to be less taxed than a normal one would, given the Fit is designed to use the 151R. There is zero lag in the start up, and I’m sure the alternator isn’t working as hard to constantly recharge it. Time will tell if this battery lasts, but I have high hopes!

4 thoughts on “Honda Fit Battery Swap – 151R to 51R

  1. Good overview thx – the video w/ cutting metal seems overkill. You lost me a bit on this though I guess when I so it it will be clear: “Maybe my particular battery was a little tall, but there were plastic edges on the right side of the full power terminal that stuck down like two stalactites – they were preventing me from sitting the connector down as much as I wanted to. I struggled trying to get it on without doing this, including using aluminum foil to make the terminal a bigger surface to clamp down on. It still wasn’t good enough, so I did have to cut those down to get it where I wanted.”

  2. Thank for this page, it helped my figure out how to upgrade my Fit’s battery. I didn’t end up using the 51R, because I think cutting the battery mount was a bad idea. Instead I spent nearly an hour at Walmart figuring out which battery could fit a little better. I discovered the EverStart 56 (8.75 x 6.00 x 8.50) which is shorter than 9in, but almost an inch thicker than the 151R and 51R. Turns out that the only modification to the Fit, is bending a little tab inward on the battery retainer bracket. That just allows you to fit the wider battery. The battery nearly fits in the slot, but it has a double sided tab on the bottom for mounting to other cars. I simply cut off both plastic tabs with a saw, then it fits perfectly into the battery slot (without the plastic box of course). So 540 CCA for $99. No mods to the fit. https://www.walmart.com/ip/EverStart-Plus-Lead-Acid-Automotive-Battery-Group-56/49988404

  3. I just upgraded a 2016 Honda Fit yesterday at Pep Boys the battery shielding was already large enough for the size of the 51R battery it fit perfectly using 10MM wrench to remove red positive first so you do not accidently short anything is number one then negative cable and the two hold down bolts I am 76 now and hands not so good their parts man assisted very kind of him kudos to PepBoys for great job done also they have many shops across the States in case you travel they are there for you!

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