Rather than running 2 med duals, has anyone put in a group 31? Seems it can be done, but wanted to know if anyone else put in a group 31 battery in their 3rd gen. Thinking of large main and small starter.

Group 34 seems to be the typical diehard, but the group 31 is significantly larger.

Tacoma Dual Battery System


Slee tray/hold down for LC100.


Group 34
Cold Cranking Amps (CCA at 0 deg.F):880
Reserve Capacity (RC):135 min.
Amp Hours at 20 Hour Rate:68

Group 31
Cold Cranking Amps (CCA at 0 deg.F):1150
Reserve Capacity (RC):205 min.
Amp Hours at 20 Hour Rate:100

I Think the Main reason people use dual batteries is so that when the alternator isn't working you can keep one doing the work of keeping say lights or a cooler powered and in any case that you run out you have the other one to crank and charge. One big battery will hold you longer, but if it dies, you're stranded.

As mentioned, this would be 1 large main and a small starter (e.g. PC680) installed ont he passanger side.

You make 2 points and I agree with the points, but I can't make sense of the common rationale.

In the case of the alternater not working, you are parked running a fridge, etc. Having more battery makes sense. You effectively have more battery for usage with a large/small setup than a med/med dual. You would never link them while parked. That means you have basically a really big starter battery if your fridge ran your battery down.

This never made sense to me, to start the 4runner you don't need that large of a battery. With an smart selenoid you can run two different batteries without issue.

Anyway... anyone put a 31M in?

I can't answer your question but I wanted to chime in here about your rationale for the big/small battery. When I started researching dual setups for my 5th Gen it didn't make sense to me either. I agree with you 100%.

I have a pretty big dual purpose battery for my main and the stock battery for my secondary. I will definitely go with a smaller battery once the stocker dies as well. The sole purpose of the second battery is to start the truck if the main is discharged. This setup has been serving me well for quite a while and works perfectly.

Maybe this can help you while planning your setup- here's mine:

Antman's Dual battery Setup

Thanks. I'll take a look at your setup. Write up looks good.

Wow, something that tall actually fits in the stock battery location without contacting the hood?
Edit: Ah, I see, that's why he's got it sitting so much further back, my set-up comes much closer to the front support.

I think you won't be able to use the Slee hold down with the 31 without some modification, it looks like it'll be too close to the front where the hood isn't high enough to clear the tall battery.

Also think about that extra weight on your inner fender, especially if you do the bumpy stuff. Having the wide hold down on top will help a lot in that respect?

Its no heavier than a couple 1200s and a lot less than 1500s which is common. Bajataco seems to use his rig, and had it running without issue for a few years.

I was thinking of just getting the slee and asking for a longer arm to the front support. That way I can drill the hole or bend it as needed. I could also make my own, but it just wont be as tidy.

Dual batteries under the hood - Page 4 - YotaTech Forums

The hood is a dome, so the posative clears more the father inboard and the farther from the front support you get. There is more than an inch between the hood mat unlatched, so I am guessing about 1/2 latched as bajataco reports closed. I'm going to get some putty and see what the real distance is. The cables reach without modification provided you get some adapters. Plenty of room for sc belt.

Either way I'll post back if it works out. These were on sale so given bajataco ran around for a few years with one, I just went for it.

To follow up... I'm running this now. Details are in my thread. Rock solid hold down, but had to modify the tray/strap quite a bit. Now that its done, Im not sure it was worth starting with the slee fj100 hold down.

Brilliant's Mod Thread

Are you still considering adding a second smaller starter battery?

Yes I have a PC680 tray. Haven't got to making a bracket to hold it in but I plan to put it on the passenger side next to the air tube and CC box. More shit to do and not enough time. I cant buy anymore tihngs until i get through my current projects.

Note you can squeeze it down on the frame rail under the main battery I think, but for now my winch solenoids take that spot. This was my original thought, and I took this for reference for people thinking of a large/small dual battery. There is a threaded penetration in the frame rail nearby to secure it.