DIY Smart Battery Box for Group 31 AGM

[bonestock]

Looking for input on how to build one of these things. I’m sure someone has done it but I couldn’t find any threads on a Group 31. Really, I’d prefer an off-the-shelf option like this but I can’t find anything stateside and these people do not seem to have a US shipping option.

https://royalbatterysales.com/catalogue/group-31-smart-marine-battery-box/

A little background, I currently have an odyssey AGM installed in the OEM auxiliary tray on the PS of my 97 LX450. It is kept charged using a Redarc BCDC25. Usually this is sufficient but, because I’ve nuked the battery so many times, it will only charge to 13.3v. Normally this is fine for a day or 2 of powering my crappy, China made 12v fridge but I’ve got a longer trip coming up.

The new VMAX 120Ah won’t fit in the OEM tray without modifications and even then I’m not sure it’ll work. VMAX MR137-120 is what I scored on the cheap and I really want to use it. Battery link: MR137-120 Deep Cycle, High performance AGM Battery-MR137-12 - https://www.vmaxtanks.com/MR137-120-Deep-Cycle-High-performance-AGM-Battery_p_28.html

I’m open to suggestions, flamming, DMs and
Anything else that gets me to a point that I can use this VMAX battery.

 

[Shoredreamer]

Is the battery too long or too tall for the OEM battery box?

 

[bonestock]

Is the battery too long or too tall for the OEM battery box?

Ha! Both I think. I am pretty sure that with minimal trimming I can get the length issue worked out. The height thing is what is keeping me from even starting. I don't want to carve up a good battery box is it's going to be too tall no matter what.

I appreciate the interest!

 

[bonestock]

According to an Amazon reviewer, a battery with my same dimensions fit in this box. This will probably be my starting point. Minn Kota 1820175 Trolling Motor Battery Power Center Marine Battery Accessory Amazon product ASIN B001PTHKMG

 

[sdnative]

Are you set on a lead acid battery? Have you considered a lithium battery, either a stand alone battery or a power pack like a Goal Zero, etc?

A GZ 1000Wh or equivalent or >=75Ah standalone battery would give you the same or more capacity than that AGM. Plus it's lighter and can be removed from the vehicle when not needed (or needed outside the vehicle). Initial cost would be higher of course, but cost per usable Ah/Wh over the life of the battery would be lower for lithium.

You would need to confirm alternator charging ability with the power packs, but the Redarc (assume BCDC1225D?) should be able to charge the standalone battery no problem.

 

[bonestock]

@sdnative - I already have the AGM battery in-hand and am looking to utilize it. Don’t get me wrong, I love to burn money but, not on this…

 

[LandLocked93]

Color me confused.
So you want to get rid of the aux batt altogether, go back to a single truck batt and have the portable batt (in the box) for ... stand-alone use at base camp? (seems like a step backwards)

Why not put the VMAX in the rear of the truck and add it to the collection? Hard to have too many points of storage for current.

 

[bonestock]

Honestly I’m not sure what is the best thing to do. I’ve got this huge battery that doesn’t fit in the OEM tray. Where would it go in the back?

 

[LandLocked93]

Guessing there is no 'build-out' going on in the back? Like compartments or drawers or anything?
If not, I'd snug it up against the back of the second row and strap it down.
Then move the RedArc back there as well.
Run a single 2ga wire from the alternator (or aux batt if you end up keeping it) to the RedArc input (red wire).
Put a 50A fuse on that run, closest to the alt or aux batt. I use marine-rate battery fuse (MRBF) devices for the convenience, but 'more elaborate' wiring can be used to facilitate traditional fusing.
Connect the RedArc to the VMAX. (brown&black wires)
Connect a 6-pot fuse box to the VMAX. (obviously a larger box for more than 6 items)
Connect everything you want to power with the VMAX to that fuse box.

Then step #6

*of note: if you keep the aux batt, you'll need a relay to take over the binding duties previously performed by the RedArc. This can be a manual, dash-switched relay or a smarter, voltage sensing type like what RedArc, BlueSea, and others offer. The cons to both are:
1) a manual relay requires action on your part to energize it so the RedArc can see alt voltage, power up, and tend to the VMAX. But you have full control over when that happens.
This is how mine is set up, tho I also utilize voltage and current monitoring to best determine when to bind the batts. I don't always bind them just to run the RedArc to charge the rear batts. Also do it to equalize the charge between the start and aux batts up front. And they usually get w/i .25V of each other with simple direct connection. (result of short distance and a non-smart alternator)

2) the auto-sense types function without your knowledge or control (unless wired otherwise). Which means that when the aux batt reaches full charge (and the RedArc is connected to the aux batt), the auto-sensor will unbind the batts - cutting off alternator voltage to the RedArc - regardless of the charge status of the VMAX in the rear. This can leave the VMAX not reaching full charge, even on a long road trip.

Given that you think your aux batt is toast, you could get rid of it and just have start and cabin batts.
Presumably you do not have failover start capability at the moment (should your crank batt go dead) with just the RedArc between the start and aux batts. You would gain this capability with the relay arrangement above (and by keeping and/or replacing the aux batt of course).

There's a bit that goes into it all, so just tried to cover the highlights.

Is the fridge all you intend to power? Or is it just the first device so far lol?

edit:clarity

 

[sdnative]

If you do install it in the back, make sure you understand the risks of charging a lead acid battery in a habited space.

 

[LandLocked93]

If you do install it in the back, make sure you understand the risks of charging a lead acid battery in a habited space.

+1 - Holy smokes is that VMAX not a sealed AGM??
If not, belay all of my previous.

 

[sdnative]

+1 - Holy smokes is that VMAX not a sealed AGM??
If not, belay all of my previous.

It appears to be AGM. Even AGM (sealed lead acid) can still vent. I am not saying don't do it, just understand the risks. That being said, I wouldn't put any variety of lead acid in a passenger space.

 

[bonestock]

Honestly, I would like to have it not be necessarily charged in the vehicle. There is no build out currently taking place. This thing is my daily driver, kid hauler and weekend warrior. I like the idea and flexibility of basically have a silent generator that I can move around by utilizing some kind of battery box. I currently have an aux battery connected to a blue sea aux fuse panel that powers everything that is not OEM (lights, aux power to back, etc.).

I'm still of 2 minds on the whole thing though... sure would be nice if this fat cow of a battery fit into the aux battery tray but, alas, maybe I should just sell it and get one that fits. When all this started, I was trying to cheap out and replace a weak Odyssey. Now, I still have a weak Odyssey and a huge VMAX that doesn't go readily fit my current setup. Dunno...

I've got a long weekend trip of stationary vehicle car-glamping coming up with my 4 year old so I'll have a projected path identified when I return (hopefully).

The real question is whether or not I can fit 35s on a stock suspension...LOL

 

[LandLocked93]

Admittedly, in the scope of available batt tech AGM is not ideal.
Very much look forward to affordable lipo.
And not the suction kind. lol

 

[LandLocked93]

Honestly, I would like to have it not be necessarily charged in the vehicle. There is no build out currently taking place. This thing is my daily driver, kid hauler and weekend warrior. I like the idea and flexibility of basically have a silent generator that I can move around by utilizing some kind of battery box. I currently have an aux battery connected to a blue sea aux fuse panel that powers everything that is not OEM (lights, aux power to back, etc.).

I'm still of 2 minds on the whole thing though... sure would be nice if this fat cow of a battery fit into the aux battery tray but, alas, maybe I should just sell it and get one that fits. When all this started, I was trying to cheap out and replace a weak Odyssey. Now, I still have a weak Odyssey and a huge VMAX that doesn't go readily fit my current setup. Dunno...

I've got a long weekend trip of stationary vehicle car-glamping coming up with my 4 year old so I'll have a projected path identified when I return (hopefully).

The real question is whether or not I can fit 35s on a stock suspension...LOL

Ah. Ok. Too much.

Could the VMAX in a box like you want fit in the area vacated by a removed OEM batt box?
Securing it while also making it easily removable may take a think. Could use the floor of OEM box as the platform.
But otherwise it's just 2 batt terminal disconnects then pull out to carry and use wherever?

 

[bonestock]

That’s an idea worth exploring! I think I’ll order another battery tray and start hacking away at it until I get it to fit.

I really do appreciate your taking the time to think about this with me!

 

[spressomon]

A little bit of wiring but use the aux battery location for starting...and put the Group 31 where the OEM battery sits ala Slee G31 battery tray/hold-down kit. Or make your own as I did.

 

[fos373]

According to an Amazon reviewer, a battery with my same dimensions fit in this box. This will probably be my starting point. Minn Kota 1820175 Trolling Motor Battery Power Center Marine Battery Accessory Amazon product ASIN B001PTHKMG

I have one of these with a battleborn 100AH lithium. There’s extra room in there for the battery. Got mine from NAPA for cheaper.

 

[bonestock]

I have one of these with a battleborn 100AH lithium. There’s extra room in there for the battery. Got mine from NAPA for cheaper.

Ahhhh lithium....

 

[LandLocked93]

A little bit of wiring but use the aux battery location for starting...and put the Group 31 where the OEM battery sits ala Slee G31 battery tray/hold-down kit. Or make your own as I did.

I get that it's doable but curious the benefits to moving the start function to passenger side.
Is it something with the Slee tray/hold-down? (ds/ps)