I use a group 34R Odyssey as my starting battery. I bought a group 27F to use as a house battery for a fridge, but figure if absolutely necessary, the 27F could be shoehorned into the stock spot in the engine compartment with some minimal adaptation or fabbing needed. Some have claimed to use a group 31, which is the next size up from 27F. With either 27F or 31, inner side of the battery is would sit pretty close to the alternator and the hot air stream from the fan.
In Odyssey world, the 27F is the "stock" battery for our 4Runners. Used to be the 34R, which is only fractionally bigger in capacity) until they bought Northstar and they consolidated the available battery sizes from both companies under the Odyssey badge. RIP Northstar batteries.

I got the tray from CBI and put a group 31 100ah battery in. https://www.toyota-4runner.org/2722723-post34.html

If you guys are still looking for an awesome battery, the lithium ion batteries are around 1800 cranking amps. There is also a built in Jump start feature.
I've sold a ton of them to Ferrari and Lambo guys, as those cars typically need plugged in because they don't drive them enough.

LITHIUM BATTERIES, MICRO'-'STARTS – Antigravity Batteries - you can read more here about them here. Call/text me at 717-319-2100 and I'll work a deal for the first few that try one.

Wow. If I owned a supercar that I rarely drove, I'd use probably use another power system to keep the computer running. Not quite sure I trust Lithium Ion all that much yet. Thermal runaway, and all. I'm probably just behind the times. Where are they made?


Edit - I can add that a Group 48 (Yellowtop DH6) battery 'fits'. Width and depths are fine, it's just about a 1/4" inch short for the stock securing bracket. 800/925/140r

A group 27f is a longer group 24 and if you shop around the RC is 165. Which puts it around 100ah.


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From my understanding the side terminals are not rated to the amps as the top posts are. I don't know it that was on Odyssey's site or full throttle.

I'll be going with a group 27f. It's pretty damn big. I'm staying away from lithium.

Also lithium batteries do not like heat. There was a good vid on YouTube explaining and testing the theory.

The 27 is 1.5”ish longer than a 24. Same height and width. Our hold down will work just like it was a group 24.


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Not saying this is a great battery. I needed a battery and went with this to try something different. Just adding it to the mix. Group48 AKA DH6. It does use a DIN post which prefers a bit smaller or adjustable negative terminal. It's a little shorter, hence the wood shim. I'll raise it from the bottom eventually. I used a lead shim from Autozone with the factory ground for now. I also took a picture that is doing no good on my phone so here it is....

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My experience is a group 27 or a group 65 is the best bang for the buck. Sadly a group 65 doesn’t have a reverse post (F mount). Unless you can up the charging voltage to match the AGM requirements, I’m skeptical of the life expectancy of an AGM batteries charge specs.

The Northstar 27F I bought a couple years ago (Now it's called an Odyssey 27F) claimed 92 amp hours on a 20 hour discharge. I bought it for my house (auxilliary)battery, but liked that it could be shoehorned into the starting battery location in case of emergency. My current starting battery is an Odyssey 34R, which requires being elevated about 1" and spacers to be added to the hold down. 24F wasn't available as an AGM at the time, so 34R it was.
Agree that if an AGM is treated to the normal charging voltage in our 4Runners, it will gradually lose capacity over time at a higher rate than normal battery aging with use. I added an HKB voltage boosting diode device which *hopefully* will allow the AGM battery to not lose so much capacity several years more down the road.

Interesting. What voltage increase are you seeing with that device? I see they made an adjustable booster that went up to plus 1 volt at one point (out of stock)

they dont like extreme cold either

I’m watching for it to be in stock also. But the GM diode I may try.


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I got the adjustable HKB.MK4 Adjustable Alternator Voltage Booster | HKB Electronics
It changes the voltage by 0V - 1V in ~.2V steps. I monitor voltage using a Scanguage II plugged into the cabin OBD terminal near the gas pedal.
I set it to + 0.6 (which is the same boost as their cheaper fixed boost unit).
At 32ºF cold start it's initially at 14.8V-14.9V with couple flickers to 15V. The 15V flickers go away after a minute or so. Later in the cold day it settles at about 14.4.
On a hot summer day, once the engine has been running a while, it goes as low as 13.8V-14.0V.
I could have bought the fixed 0.6 boost unit and saved some $$....live and learn.

Thanks for the info. My UltraGauge currently shows a max of about 14.23 with a stock Alt. Do you think it would be worthwhile to pop a fixed volt boost unit in to help out my new AGM battery? The variable unit is out of stock.

When I plug in make/model year this is the only unit they have in stock MK3 Mini blade 7.5A (Electronic fuse version) (Micro blade compatible) | HKB Electronics