Battery Box Size in 2021 320S

jimrj

Our 2021 320S arrives soon. I want to upgrade the battery but need to know the size of the standard battery box/hold-down that comes from the factory. Any one the dimensions?  Another question—Will a Group 27 battery fit In the standard box or will I need to also upgrade the box?  Where would one buy the larger box?  Thanks for the help!

VictoriaP

I can’t answer your 2021 specific questions, but battery boxes are readily available at any auto parts store, big box stores like Target, and online retailers like Amazon. 

You might call your dealer about the rest. I negotiated a battery upgrade that was installed before I picked up my 2019. 

Denny16

Why don’t you just have the dealer install the larger battery instead of the Group 24.  The new front bin will hold two group 24 batteries, like two 6-volt 100 amp AGM batteries wired in series, or a larger 12 VDC AGM.  That way you just pay the difference, instead of getting something you are going to replace.
cheers

Sharon_is_SAM

@jimrj - are you asking about the dimensions of the front tub for the 2021?  Otherwise, in the past, pre- 2021 owners have replaced their Group 24 battery with a group 27 in the plastic and aluminum tub without any problems.  The new aluminum tubs are much larger, too.

DougH

@jimrj ; Howdy and Welcome!  A single 13" x 7" 125Ah Group 31 (75lbs instead of 50-55lbs for a 85Ah Group 24 10.2" x 6.6" AGM) fits in the old tub too, but you'll need a bigger box.  Or you can go half way between and put in a 100Ah Group 27 (12" x 6.7").  An AGM type battery will be more $$ than the cheap ones you have to refresh periodically with distilled water.  But most on this forum spring for the AGMs.  If the 2021 tub is even larger front to back you should be fine...  but someone with a new one and a tape measure should verify that.

The standard box for Interstate Group 24 battery is 11" by 8" at the top and rests between two pieces of horizontal angle iron (11" apart) that also support the propane tank cage.  That box wont fit a 27 or 31.  And the 12 or 13 inch long batteries won't squeeze between the existing angle iron braces, at least not on my 2017 model.  To fit the Group 31 you can just run two pieces of angle iron 7.5-8" apart and 14" long front to back on top of the existing side to side rails, to fit a larger Group 31 box, and attach them to the existing rails (weld or bolt). 

A Noco or similar tray is $10 and a new box is $20 for whatever size you go with, but it needs to sit on a stable platform that won't move in an emergency situation.

But as mentioned, try to have the dealer put in the 27 or 31 to save some money, and possibly make less of an environmental impact.

Old battery, a Group 24 standard in most RVs...

jimrj

Thanks all for the comments.  They're helpful!  I'll work with the dealer.  My goal is to save as much space in the front tub of the 2021, but also to have a battery that's good for some boondocking for a few days.  Right now, I'm tentatively thinking of a single 12V deep cycle AGM, Group 27 battery as an upgrade to the dealer-installed Group 24. Again, thanks for your comments.

pthomas745

I have my eye on the same kind of AGM battery for a replacement for my now 4 year old battery.    What has intrigued me lately is reading about how an AGM battery can be installed in any position, except upside down.  So, instead of spreading out a battery on precious floor space, it can be mounted standing on the shorter end.  Many boaters apparently mount their batteries this way, so it isn't unheard of.  I mentioned this a few weeks ago and one down side could be the weight profile of the battery on the base of the tub, so I will probably find something to provide a bit of support. 

Denny16

Another is how the venting valve on the AGM is designed.  Whilst the battery can be tipped and angled for short periods of time, it has a correct mounting orientation, check out the manufacturer install specifications.  A Marine AGM is different design to the AGMs used in RV trailers.
cheers

mntrails

Here's a photo that may help - the tub on the 2021 320s measures 14.5" back to front at the shortest dimension.  Inside, the rear wall is 1" deeper at the top and ~5.5" deeper at the bottom, i.e. it angles backwards toward the bottom. There is a piece of Al angle at the bottom  running side to side roughly at the 14.5" mark.  A type 27 box fits fine front to back.  The boxes you see are both Nocco boxes.  I tried a combo box that fit up to type 31 and it was too long for easy lid removal.  The top of the type 27 box in the picture measures ~16.25".  The other box is a type 24.  There's a lot of room in the tub and a single battery can also be rotated 90 degrees allowing bigger sizes to fit easily.

I got my extra box from Batteries Plus.  As far as mounting goes, the bottom of the tub is solid Al sheet and as long as you take care to check what's underneath, you can fasten the box(es) with sheet metal screws in almost any location.

Having the dealer put in what you want is a great idea.  In my case, I happened to have an extra type 27 in-hand and the dealer was passing the full cost of a type 27 upgrade on to me so I just took the standard type 24 and am using this hybrid arrangement to learn on.

jimrj

That helps.  Thanks!

Denny16

Not a very nice dealer, if they didn’t give you a credit for the smaller battery they were providing anyway, they should just charge you the price difference between the original battery and the larger one.  If you are ordering or buying a new trailer that you should be able to get it fitted with the bits you want.
cheers

jimrj

Yes, they will be giving me a credit and will be charging me the price difference between the two. I was unclear about that in my earlier post. Thanks!

Denny16

Good, glad you got it sorted.
cheers

DougH

@jimrj Sorry to mention this if you've already searched this forum for "battery monitor", but you could consider getting one or making sure you don't dip below 12.0V too frequently... to make that battery last quite a few years.

These are "deep cycle" batteries that can be brought down to 10-20% and charged back up to full, but many large volume AGM manufacturers list how many recharge cycles are possible, within a given percentage of the rated charge capacity, plotted against depth of discharge.

For VMAX batteries sold on Amazon, they've lowered the numbers... but they are listed on bargainshore as...

1. Number Of Cycles       Depth of Discharge
2. 300                                100%
3. 600                                  75%
4. 900                                  50%
5. 1500                                25%
6. 3500+                              10%

Another grid energy site listed this comparison of lifespans for continuous use, letting batteries get 50% discharged versus 30%



Again, apologies if you were already well aware.

Denny16

Good charts, yes I knew you could discharge AGMs below 50% without damage.  Our original battery was often discharged down to within 20-30% remaining capacity by the TaB’s previous owner, and after two years, the OEM batrery needed replacement.  The 50% discharge limit is a carry over from lead acid batteries, and to get the maximum life out of a battery, as your chart shows.  keeping it above 30-40% seems like a good compromise between use and battery life.

Bottom line though, a Lithium battery can be more consistently discharged down to 20% without loss of recharge cycles, has a greater charge/discharge cycle life and is lighter than the same AmpHr AGM battery, so lithium batteries do have some advantages, and when adding battery capacity to a small trailer, weight and size five the advantage to lithium. Especially on a 320 feint tongue battery box location.
cheers