Battery Box Sizing Question and Issue

[glendodom]

I have a 2018 3721RL which I received in Oct 18.

My unit came with one 31 group size battery installed. Since I am running a residential refrigerator, I had thought about putting a second battery in. The battery box which Montanna installed in the unit is an oversized box with connectors on top of the box. The box id is about 12 x 13 which is fine for a 31 group but after doing some research this box seems to be large for a single battery but not large enough due to width for using 2 of any size, 6 volt or 27/29/31. Best I can figure all the 27/29/31 group sizes all run about 6.75 - 6.81 in width and 12 - 12.75 in length.

Does anyone else have this unique size battery box which came installed with their unit? If so what type battery configurations are you using?

Also another issue I have found in doing my checking, the box has a bottom drain spout which the factory cut a hole in the bottom of the storage floor for its placement. The box bottom has a series of ridges at the bottom allowing any spill over to be at a lower point that the bottom of the battery. During installation, the factory drilled two holes in the bottom of the battery box at the lower points thus when having any spillover it over times corroded the two screws thus allowing the corrosive liquid to leak out onto the bottom side of the storage area and naturally causing a corrosive mess. I have cleaned it all up and removed the corroded screws and plugged the two holes within the battery box. Unbelievable!

[gjennings]

Sounds like the same box they installed in my 2019 3791RD and the dealer installed 2 SMR-27 Interstate 12V batteries in mine. I have since removed the box and have installed 4 lithium batteries.
I do like the box tho and having the connections like it does.

[glendodom]

Originally Posted by gjennings

Sounds like the same box they installed in my 2019 3791RD and the dealer installed 2 SMR-27 Interstate 12V batteries in mine. I have since removed the box and have installed 4 lithium batteries.
I do like the box tho and having the connections like it does.

Looking at Interstate's website it shows the SRM 27 as 6.75 width. Two of them would be 13.5 and the best I can get out of my box id width is 12.5 at best. I may need to just go do some checking on actual 27 group battery size. The 31 that is in there is 6.75 width. Seems I have an odd size box if it is suppose to fit 2 of the 27s.

[rohrmann]

Just to correct some bad information, the factory does not install batteries or boxes. These are installed by the original selling dealer when they prep the unit when it is sold. Our dealer installed two boxes for group 24 batteries and the boxes had the drain hole that required holes to be cut in the floor of the front compartment. Several years ago, I upgraded to larger batteries and had to replace the boxes with ones that would accept the larger batteries, and also had to cut new holes to fit the drain part of the boxes.

[gjennings]

Not sure it matters who did the install. He was wondering if 2 batteries would fit or not.

[Arkware]

I had the same box with 2 group 24 batteries, dealer installed. They tried to give me only one battery, but my understanding is the Res. Fridge rigs should have at least 2 batteries.

Last year I also upgraded to 4 GC-2 6 volt batteries. Had to get a new box for those anyway. Very happy we upgraded.

What ever choice you make, I suggest you look for "true" deep cycle batteries.
The clue while looking on-line is they will be rated in "Amp Hours" instead of "Cranking Amps".

[jimcol]

I have no idea if this is true but I was told the holes in the bottom of the box were necessary. They are required so the vent on top of the box will draw in the event the battery off gases,

[twindman]

This is a little off topic, but here is a question. Since they ship the units with no battery, how do the breakaway brakes work when they are delivering them? I am guessing they don't. Just curious.

[DQDick]

Replace with AGM batteries and forget about the drains.

[jeffba]

Originally Posted by twindman

This is a little off topic, but here is a question. Since they ship the units with no battery, how do the breakaway brakes work when they are delivering them? I am guessing they don't. Just curious.

I would think the transporter would supply one

[PeteandJoan]

Originally Posted by DQDick

Replace with AGM batteries and forget about the drains.

X2 what DQDICK said.

[glendodom]

Originally Posted by DQDick

Replace with AGM batteries and forget about the drains.

My inverter only runs the refrigerator.

What brand AGM battery and size are you using?

I reviewing various AGM batteries, SAM's has a Duracell 31 at $179 and a 34 at $119. First I had heard of a 34 group but it is noted for Marine/RV and is a little shorter than the 31. Not sure why the big price difference?

Thanks, Glen

[jdarwin]

Originally Posted by rohrmann

Just to correct some bad information, the factory does not install batteries or boxes. These are installed by the original selling dealer when they prep the unit when it is sold. Our dealer installed two boxes for group 24 batteries and the boxes had the drain hole that required holes to be cut in the floor of the front compartment. Several years ago, I upgraded to larger batteries and had to replace the boxes with ones that would accept the larger batteries, and also had to cut new holes to fit the drain part of the boxes.

I'm interested in adding a 3rd group 24 battery to get up to 240 AH. Where can I find a box large enough to hold 3 batteries? Any suggestions?

[Rod Spohn]

Originally Posted by jdarwin

I'm interested in adding a 3rd group 24 battery to get up to 240 AH. Where can I find a box large enough to hold 3 batteries? Any suggestions?

I'm also looking to add a couple batteries and have been looking for a bigger battery box. I've found if money isn't a factor then you can find what you are looking for. But, I've about decides to just add another box and link the vents. It will be interesting to see what others have found and used.

[AZ Traveler]

I installed 2 Noco dual 6volt battery boxes - about $75 each. Available from Walmart, Batteries plus and Amazon. The group 24 batteries are low capability - I would stay away from them. It is best to install batteries as a set vice adding to already installed batteries. Six volt batteries are generally more powerful and last longer than 12 volt models.

[Carl n Susan]

Being frugal (aka cheap) I use Dyno boxes and add vents as needed. They come in different sizes capable of holding one to four batteries. I have multiple battery boxes and just join the two vent hoses into one using a PVC coupler.

Here is a link to one place that has the Dyno boxes. There are more. *Clicky*