It's 30 second of hacking with aviation shears.

My tray has adequate length on one side, but not the other side, and the side with adequate length has a ridge that extends up from the bottom that would have to be trimmed away. What I'm concerned about it that a 51R battery will bring the negative side of the battery very close to the heat sink for the ECU I think it is. Maybe only 2 or 3 mm, if not actually touching it. Perhaps the battery might interfere with cooling of the ECU

I doubt it would interfere. There is flex in the tray. Just tighten it down in the right spot. Look at Rontiki's photo a few posts ago.

It's interesting that some have a smaller tray and some, like mine, appear to be sized for the 51r. The year of manufacture didn't seem to make a difference. Any correlation to where it was built? My car was built in Japan.

A wild guess that Mexican made Fits have the smaller tray and the Japanese made ones are using a Japanese spec tray which is the larger one. This might imply that the Japanese Fits/Jazz cars might be coming with the larger battery out of the factory. We'll probably never know for sure unless someone in Japan pops up the hood and takes a look for us.

I believe the Japanese cars have LED headlights which have yet to appear on the North American version which is in line with my belief that better cars are being built/sold in foreign markets whereas North America is now considered a market where you build/sell cheaper cars. That's a complete flip from say 50 years ago when the best cars were built/sold in North America. The world has changed.

Mine has the non-rectangular, smaller tray; is made in Mexico.

Even after loading it into Photoshop, displaying it full size, and adjusting the levels of black and white, I can't tell much for sure from Rontiki's photo. It does however look like the battery is only a few millimeters from the heatsink, at the top of the battery. How close it is as you move down the battery toward the tray is hard to see; it's too dark, or obscured by the angle of the shot, or both. I don't have enough skills to analyze it better, translate what is going on in 3 dimensions, from looking at, and taking measurements from, the 2-dimensional photo. I will say that things in the engine compartment are laid out at a variety of angles. The days of things being, for the most part, laid out parallel to each other or at right angles, in 3 dimensions (from front to back, side to side, and top to bottom), are gone. Many things in the Fit's engine compartment seems to be placed at their own unique angle. So while the battery and the heat sink may be a few millimeters apart at the top of the battery, I wouldn't be surprised if they are closer together at the bottom of the battery - where I can't see. I don't think there is any room at the right side (right when you are facing the front of the car) of the battery to slide the battery any further to the the right.

I'm pretty sure you're overthinking this. If you have the smaller tray, the answer is either cut it or replace it with the larger tray assembly.

Perhaps Rontiki can chime in on the fitment close to the heat sink to alleviate your concern.

sneefy, I took a look at it again and I saw that there is a ground wire at the front of the battery that keeps the battery from moving forward about 5 mm or so closer to the vertical sheet metal where the cable is connected, because the ground connector is sticking out at about a 30 degree angle from vertical rather than lying flat against the body surface, so all I would have to do in order to move the battery forward about 5 mm (and gain 5 mm at the rear) would be to bend the ground connector flat against the body. It would also be possible, though a lot more work, to connect the ground cable somewhere else. With the screw head removed, that would give me about 7 mm. However there is also a bunch of wrapped together wires about a cm in diameter at the bottom of the tray, at the front, pushed right up against the tray, and quite firmly - I can't pull it away with my fingers. Not sure how much effort it would take to move it so as to allow the battery to move forward. A contemporary sealed battery isn't likely to leak its acidic solution so I don't think it is necessary to have the kind of tray that holds water to a depth of about 5 mm. I think the tray could be removed entirely and just a flat piece of non-conductive plastic would be sufficient to keep the battery from resting on body panel sheet metal. Why is the oem tray sized for a size 51 battery, except for a roughly 8 cm by 6 cm part at the right rear of the tray that is non-extant? I don't think that there is any battery made for the shape of that tray. Did they have something else in mind to put in the empty 8 cm by 6 cm area that sticks out about 6 cm at the rear?

So yes, I think there is a good chance I could move the battery forward enough to get at least 5 or 6 mm clearance between the battery and the ECU heat sink.

Good. Glad it looks like it will work for you without too much difficulty.

​​​​​​I am pretty sure that I have the battery as far forward as the tray allowed for. It is very secure and no chance of it sliding closer.It seems the clearance between the heat sink and the negative terminal are adequate for air flow. Perhaps the negative could be rotated to gain a little more clearance, but I'm comfortable saying it shouldn't be a problem. Thanks all for the comments and suggestions

2016 EX will take a 51R.

That was the first thing I noticed when we got it. They changed the way it is mounted making room for a larger battery. We have never had to replace a battery on the 3 Fits we have owned, but when we do it will be a 51R.

I wish I'd stumbled across this thread before I replaced the battery in my 2015 EX a few months back........:mad:

A. Confirmed that some models' battery box = a bit small to fit the 51R battery. Will need modification to fit. My car = 2015 Ex (Mexico) and comes with the small size battery box. Here is the image:
https://cimg1.ibsrv.net/gimg/www.fit...05dc10c2c4.png


B. And for those who are lucky enough to get the larger battery box: Picture from Musicalpa @ 2016 Fit Battery Reliability

https://cimg1.ibsrv.net/gimg/www.fit...35532a3edb.jpg
No need to mod/cut, just put the 51R battery in, try not to have the battery touches the heatsink and you are good.

could you tell us what you do/how it goes with pictures? i have the same car as you

I believe people just hack/cut as illustrated by this red line



https://cimg0.ibsrv.net/gimg/www.fit...7a57162677.png

$102.99, I think I'm gonna go with this one, when/if my battery finally gives up:

https://www.napaonline.com/en/p/NBP6551R

I didn't cut the fit battery box, as I had an old 2003 accord battery box laying around which I modded to put the 51R battery into instead.
1. Hacksaw - Cut bottom pin to the front, use crazy glue n baking soda to fill-up the hole. - Hack a little off the upper corner plastic toward the headlight, to allow me to move the battery box forward.
2. Heatgun - To soften the lower corner toward the headlight, so I can mold the plastic n push the tray a little more to the front, that way I will have at least 1/2" gap between the battery cover (original from the Fit) and the heatsink(toward the windshield).
Final result with 51R Interstate Battery @ Costco = $72.99 + tax etc. Total was around $83 with the core exchange:
https://cimg8.ibsrv.net/gimg/www.fit...4f49beb702.jpg
Gap between heatsink and battery.
https://cimg9.ibsrv.net/gimg/www.fit...a9c6646243.jpg


If I m to cut, i would do it like this:
https://cimg2.ibsrv.net/gimg/www.fit...42430c0e9a.png

I replaced my old battery with new 51R few weeks ago. Just simply remove what was obstructing bigger size of 51R [carbord insulation wrap+plastic undertray] and there was absolutely no problem to fit battery in and use original attachment bracket. Even noticed verticaly was even more space to place it nicely off all chassis parts. Plastic no need to cut is there collect the dust and water anyway.

thnks fibreP..good writeup

FYI, if you want the exact information here it is: the 51R will fit native in the tray of fits built in Japan. the Japanese tray part is the full sized tray without that notch shown in the picture from the previous poster. The Fits built in mexico, with the mexico tray part number is the one with that cutout thing area. i know because i just bought the japanese tray part for my 2015 fit built in mexico. and its sitting next to me.

About how much was the Japanese full sized tray?