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Open Roads Forum  >  Do It Yourself Modifications and Upgrades (DIY)

 > Adding a new battery...questions....(venting/gassing)

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SJ-Chris

San Jose, Ca

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Posted: 03/04/21 01:21am Link  |  Quote  |  Print  |  Notify Moderator

I've got two 2015 Thor Majestic 28a Class C RVs. One of them now has two AGM Group 29 batteries (I believe they are Group 29s) for the coach. The other RV has two lead acid Group 29s. All the batteries are ~1 year old. I'd like to add a 3rd battery to each RV (an AGM to the RV with the AGMs, and a lead acid to the RV with the lead acid batteries).

The easiest place for me to put this 3rd battery (perhaps the only convenient place) is in the passenger side front compartment. This compartment is a decent size (~1 foot tall, 4 feet long, and 2 feet deep). I currently store the welcome mat, a 9'x16' mat, some campfire supplies (lighter, etc) and a pop-up garbage can for the campsite.

Note: The other two batteries are on the driver side.

I checked the compartment regarding adding the extra weight of a battery. I'm confident it could hold it without any problem, but I like to go overboard on safety so I will be adding some extra metal strapping underneath.

My question is regarding venting the compartment and battery gassing. I'd like to put this battery in a battery box like this, and then secure it in the back of this compartment:
https://www.amazon.com/attwood-9084-1-Large-Battery-Box/dp/B0000AY9DQ/ref=sr_1_2?crid=3ETMNZURVN47I&dchild=1&keywords=battery+box+group+31&qid=1614843096&sprefix=battery+box%2Caps%2C281&sr=8-2
That way, there would never be any risk of anyone shorting any metal across the top of the battery (yikes!). My plan is to mount it near the rear of the compartment so it will mostly be out of the way. I will drill some holes in the side of this battery box for the battery cables and then the battery cables will route out the back of the compartment and over to the other two batteries on the driver side.

What sort of venting do you think I need in this compartment (not the battery box, but the actual side compartment where the battery (in its battery box) will live))? Will 3-4 half inch holes near the top and bottom of both ends of the compartment do the trick? Do lead acid and AGM batteries gas a lot? If so, will they cause any damage to any items that are stored in this compartment along with the battery (like the items I mentioned above)? Should I also drill some vent holes in the battery box? Should I worry that drilling some holes in this compartment make it no longer waterproof?

Not sure if I'm overthinking this or not. Figured I could learn from those much wiser here :-)

Let me know what you think.

-Chris


San Jose, CA
Own two 2015 Thor Majestic 28a Class C RVs

2112

Texas

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Posted: 03/04/21 04:52am Link  |  Quote  |  Print  |  Notify Moderator

Use a vented box and hose. THIS May provide some ideas. See the 2 white boxes with the black vent hose.

HERE is a wall mount vent. See the Frequently Bought Together section


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drgslayr

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Posted: 03/04/21 07:39am Link  |  Quote  |  Print  |  Notify Moderator

We had a Majestic 24a. When I added an extra battery we didnt have the storage space to loose so I added one of these.

We went with AGM so we didn't have to worry about adding water or anything else.

https://www.torklift.com/rv/hiddenpower.

pianotuna

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Posted: 03/04/21 08:14am Link  |  Quote  |  Print  |  Notify Moderator

Unless the batteries are almost unused, adding a 3rd battery may not be a great idea. If you can afford it, replace all three.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

jdc1

Rescue, Ca

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Posted: 03/04/21 09:35am Link  |  Quote  |  Print  |  Notify Moderator

A Prius has a 1/4" hose for their battery vent. That battery is in the passenger compartment. This may tell you something. I believe Toyota might have better engineers than trailer manufactures, so I would think a 1/2' or 3/4" hose attached to your battery box and plumbed to the exterior would be sufficient.

jdc1

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Posted: 03/04/21 09:37am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Unless the batteries are almost unused, adding a 3rd battery may not be a great idea. If you can afford it, replace all three.


Or, put the 4 older batteries on one bank, and the 2 new batteries on a separate bank.

CA Traveler

The Western States

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Posted: 03/04/21 10:52am Link  |  Quote  |  Print  |  Notify Moderator

The battery box should be sealed with 2 vent hoses one high and one low.

Seperating parallel batteries (if that is your plan) by 8' means unbalanced batteries ie load/charge usage distribution will be unequal. You might want to research this.

Have you considered switching to 2x GC batteries instead?


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SJ-Chris

San Jose, Ca

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Posted: 03/04/21 11:33am Link  |  Quote  |  Print  |  Notify Moderator

2112 wrote:

Use a vented box and hose. THIS May provide some ideas. See the 2 white boxes with the black vent hose.

HERE is a wall mount vent. See the Frequently Bought Together section


I found that article to be interesting. On the one hand, it talked about the seriousness (...and explosions), and on the other hand they seem to conclude with this: "Although it sounds fancy, and rather technical – venting an RV battery is not quite as complex as it sounds. All you really need to do is add a few holes – about 25mm in diameter to the top and bottom of your battery enclosure. It’s a simple enough procedure and it could prevent a disaster."

Does anyone know what impact gassing/etc might have on other belongings stored in the same compartment?

Thanks!
Chris

SJ-Chris

San Jose, Ca

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Posted: 03/04/21 11:38am Link  |  Quote  |  Print  |  Notify Moderator

drgslayr wrote:

We had a Majestic 24a. When I added an extra battery we didnt have the storage space to loose so I added one of these.

We went with AGM so we didn't have to worry about adding water or anything else.

https://www.torklift.com/rv/hiddenpower.


That is a very interesting option which I had not thought about....THANKS for the suggestion.

I did some more searching around and found this also:
https://www.amazon.com/Steel-Bolt-Battery-Mounting-Tray/dp/B076666P81/ref=pd_aw_sbs_1/144-3145342-8767014?_encoding=UTF8&pd_rd_i=B076666P81&pd_rd_r=f1726189-410c-4871-b170-b3d24a36a906&pd_rd_w=BEsmu&pd_rd_wg=CqbHc&pf_rd_p=1b60d0cd-e691-440f-aa83-cc788b983d0c&pf_rd_r=WHJTWV7J842SEVSR758V&psc=1&refRID=WHJTWV7J842SEVSR758V

I'll have to crawl under my RV and see if there is a convenient place for something like this. The one drawback I see is access....seems like it would be a tremendous hassle anytime the battery needed to be checked/maintained/etc. If I was able to mount such a bracket, I'm not entirely sure how I'd be able to lift the battery up into it.

-Chris

SJ-Chris

San Jose, Ca

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Posted: 03/04/21 11:57am Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

The battery box should be sealed with 2 vent hoses one high and one low.

Seperating parallel batteries (if that is your plan) by 8' means unbalanced batteries ie load/charge usage distribution will be unequal. You might want to research this.

Have you considered switching to 2x GC batteries instead?


I'm using some heavy gauge wiring to connect the batteries. I plugged it into a voltage drop calculator and it seems reasonable. I'm no expert, and please correct me if I am wrong, but during the final stage of battery charging the current is pretty low (just a few amps going into the battery). When the amps are low like this, there is very little voltage drop. I suppose it is possible that one battery (closest) could get finished charging a bit sooner, but with solar doing lots of charging everyday it seems like the furthest battery would easily get caught up. Not sure, but the difference could be quite minor.

Regarding using 2x GC batteries...A good suggestion. However, right now I've got two Group 29s that each are at ~100AH. Adding a 3rd will get me to ~300AH which is what I'm looking for. Two GCs only gets me to ~225-230AH.

Part of my reason for adding a 3rd battery is that I also am installing a 2000w pure sine wave inverter. It will mostly just be for TV/DVD, computers and misc items, but also I want to be able to run my 900w microwave. From what I've read, two batteries might not be quite enough so I like the idea of adding a 3rd battery which will increase my capacity by 50% and spread the high amp draw out by 33.3%. For example: With 2 batteries and assuming the microwave will draw 100 DC amps through the inverter, each battery would be supplying ~50amps. By adding a 3rd battery, each one would only be supplying ~33.3amps which to me seems a lot easier on the batteries, wiring, etc. I have a parallel set of 3 AWG wires going from the batteries to the inverter to minimize voltage drop also.

-Chris

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