Group 24F Battery Installation

My OEM battery died: 87,000 km but only 31 months old.

I wanted to install an AGM (Absorbed Glass Mat), mostly due to supposedly better lifespan with longer warranty. I went to my local Costco seeking a Group 35 AGM battery but, finding no Group 35 AGM batteries I took another look at the battery tray in the CX-9 and decided a 24F would fit - after a few minor modifications.

I removed the cover from the positive terminal connection block and connected the positive terminal (orange wire) and engine ground (blue wire) to a 12 volt battery from my lawn tractor. This keeps the electronics 'alive' while replacing the CX-9 battery - that way I don't have to re-program all the settings stored in memory.


Using a 10mm wrench or socket, disconnect the negative terminal (black cable) from the battery first, then the positive terminal (red cable). Loosen the two battery hold down 'J' bolts (also 10mm), unclip from the brackets, remove the hold down assembly and set aside.

Group 24F vs OEM Group 35. 24F is about 28-30mm longer, but almost exactly same width and height. The 24F case is ~255mm in length.

There's approximately 243mm between the plastic protrusions on each end of the battery tray, but the distance to the ends of the tray is just slightly under 270mm total inside length - lots for a 24F!

The protrusions are in awkward spots to remove with most tools. An oscillating tool is VERY handy for making these cuts. If you don't have one I'd suggest borrowing one if you can. A hacksaw blade could probably be used, either with a holder that grips only one end of the blade, or just a bare blade (though your hands will need protection from the teeth).

Here I'm cutting the protrusion flush with the bottom of the tray. Notice the angle of the blade relative to the tool.

I don't have a photo of the vertical cuts on the front of the tray, but on the back there's not enough room to cut from the top, so I cut from the side - flush with the inside of the battery tray. If you're using a hacksaw blade you may want to remove the entire tray from the vehicle to make the cuts.

Notice the position of the blade - one of the great things about these tools is that you can rotate the blade into a variety of positions to make cuts in places no other saw can get into.

This is the rear edge of the battery tray, showing where the tabs had been.


Insulating box / sleeve modifications. Sorry, no photos prior to this one.

I cut the box midway down each of the long sides, then added some thin black foamboard to the outside of each. These were the original length, plus an additional 28mm.

This photo shows the two pieces of the box flattened. The shiny strips are fairly strong 2-sided tape to hold the foamboard.

I cut each of the two pieces of foamboard 264mm x 172mm, IIRC.

This the assembled insulating battery box / sleeve on the 24F battery. It was VERY snug. If I did it again I'd either extend it by 30mm (instead of 28mm) or, more likely, start with a sheet of Corplast corrugated plastic and build an entirely new box to fit the battery.

Note Gorilla Tape reinforcement on corners of box. I hope it stands up to the heat of the engine compartment - I guess I'll find out soon enough!

This is the Group 24F AGM battery installed. It looks like it was designed to fit there.

I believe both flooded and AGM Group 35 batteries are often better than the OEM battery. Compared to a flooded battery, the AGM battery I bought has roughly 11% more Cold Cranking Amps (710 vs 640) and Cranking Amps (885 vs 800). Reserve Capacity is 120 minutes vs 100, and Amp Hours are 70 vs 57. I suspect most of that is due to the increase in size from the Group 35 to 24F (~12% increase in length).

The only specs I could find for the OEM Panasonic battery show the following - but I don't know if the rating is consistent with North American batteries:
Cold Cranking Amps: IEC 350, JIS 533
Reserve Capacity: 118 minutes
Amp Hours: 70
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Great write-up - upgrade went exactly as described.
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