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

[SJ-Chris]

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

[drgslayr]

SJ-Chris wrote:

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

That is why we went with AGM batteries, nothing to maintain.

I have a Harbour Freight Motorcycle lift I used to lift the box into place.

[SJ-Chris]

SJ-Chris wrote:

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

The torklift solution looks like it costs over $200. Would be nice to find a less expensive solution.

This looked like a good solution (I like all the mounting holes), but it isn't big enough for a Group 29 battery: $48
https://www.amazon.com/Steel-Bolt-Battery-Mounting-Tray/dp/B076666P81/ref=pd_sbs_1?pd_rd_w=0sM5W&pf_rd_p=527ea27c-adf6-4b67-9c5f-265eb29e0622&pf_rd_r=ABK60C0DF1AWM22PBZ97&pd_rd_r=51e07f18-ddeb-415c-b1a6-a27605c30b6c&pd_rd_wg=sYElr&pd_rd_i=B076666P81&psc=1
Has anyone seen something similar that will fit a Group 29 battery? (Group 29 battery is 13" long by 6.75" deep by 8.5" tall). This is really the style I'd like to find.

I googled for a bit and found this: $89
https://www.steinertractor.com/OLS035?crawlparam&gclid=EAIaIQobChMIgdXbgpub7wIVpCGtBh0HfgxOEAYYByABEgLjgfD_BwE
Looks like it could work, but would require drilling several mounting holes through the back plate. Should be doable.

Gonna keep looking though...

-Chris

[SJ-Chris]

pianotuna wrote:
Chris read the information at the smart Gauge site re voltage differences.

Do you have a link? I googled a bit but it didn't seem like it was pointing me to the right place.

[pianotuna]

Chris read the information at the smart Gauge site re voltage differences.

[SJ-Chris]

I'd suggest that a 900 watt microwave may draw about 100 amps. I know my 1570 watt Dometic draws 185 amps.

I was able to successfully operate the Dometic microwave on 3 Marine jars for more than a few minutes. I have two banks--and one was 3, the other was 4 batteries. Switching allowed me to do either/or/both/off.

100 amps is what I was assuming from my 900w microwave.

Question: Are you saying you were able to run your 1570w microwave for several minutes with 3 batteries? If so, then it seems like I should not have a problem running my 900w microwave for even longer.

I guess I'll find out and report back.

-Chris

[SJ-Chris]

pianotuna wrote:

CA Traveler wrote:


Are you sure? Method 3 requires equal amps and voltage from all 3 batteries. How are you doing this with one battery located 8' away?

A 900W MW draws 65A+ and not the best for starting batteries which a Marine battery is - ie a compromised starting battery. Might be OK and might cause a low voltage fault.

Hi CA Traveler,

He could do method #3 if the leads to the battery bank go to a buss bar that is 5 feet from any battery. i.e. all wires the same length.

I'd suggest that a 900 watt microwave may draw about 100 amps. I know my 1570 watt Dometic draws 185 amps.

I was able to successfully operate the Dometic microwave on 3 Marine jars for more than a few minutes. I have two banks--and one was 3, the other was 4 batteries. Switching allowed me to do either/or/both/off.

Yes, Method #3...All my positive wires are connected on a buss bar, and all my negative wires are connected on a different post...HOWEVER...the wire lengths are different. It's the best I can do currently. I'll do a voltage check at each battery to see if there is a difference when the batteries are in bulk charge (highest amps trying to enter batteries and therefore largest potential voltage drop). If one of the batteries is significantly lower in voltage (...how much is too much? 0.2v? 0.3v?) I can run a 2nd cable to that battery and I suspect that will fix the issue.

Actually, the two batteries that will be added (one already added) have much longer wires BUT the cables are a fair amount thicker so that will help already with any voltage difference during charge.

Make sense?
Chris

[pianotuna]

CA Traveler wrote:


Are you sure? Method 3 requires equal amps and voltage from all 3 batteries. How are you doing this with one battery located 8' away?

A 900W MW draws 65A+ and not the best for starting batteries which a Marine battery is - ie a compromised starting battery. Might be OK and might cause a low voltage fault.

Hi CA Traveler,

He could do method #3 if the leads to the battery bank go to a buss bar that is 5 feet from any battery. i.e. all wires the same length.

I'd suggest that a 900 watt microwave may draw about 100 amps. I know my 1570 watt Dometic draws 185 amps.

I was able to successfully operate the Dometic microwave on 3 Marine jars for more than a few minutes. I have two banks--and one was 3, the other was 4 batteries. Switching allowed me to do either/or/both/off.

[CA_Traveler]

SJ-Chris wrote:

pianotuna wrote:

SJ-Chris wrote:


I believe all the batteries are about 14 months old. To me, that makes them relatively newish. Assuming they are all in good health, I'm willing to add a 3rd battery which is brand new (same manufacturer/size/etc).

-Chris

Please at least wire the new batteries in a balanced manner. Method #3 is the only way to do so for odd numbers of jars.

http://www.smartgauge.co.uk/batt_con.html

I suggest adding some plywood to the compartment you are going to use--and if all 3 batteries will fit there it would be better.

I am happy to say I am using Method #3.

Are you sure? Method 3 requires equal amps and voltage from all 3 batteries. How are you doing this with one battery located 8' away?

A 900W MW draws 65A+ and not the best for starting batteries which a Marine battery is - ie a compromised starting battery. Might be OK and might cause a low voltage fault.

50% SOC batteries start charging in bulk and ramp up to absorb with about 14.4V and certainly are drawing more than a few amps. They stay there until the absorb stage starts to taper amps.

Any old charger and any wiring situation will eventually get the batteries charges. But there are cons including longer charging, shorter life and lower voltage under load. What you are doing may work for you. Sometimes it's try it, see and learn.

[SJ-Chris]

pianotuna wrote:

SJ-Chris wrote:


I believe all the batteries are about 14 months old. To me, that makes them relatively newish. Assuming they are all in good health, I'm willing to add a 3rd battery which is brand new (same manufacturer/size/etc).

-Chris

Please at least wire the new batteries in a balanced manner. Method #3 is the only way to do so for odd numbers of jars.

http://www.smartgauge.co.uk/batt_con.html

I suggest adding some plywood to the compartment you are going to use--and if all 3 batteries will fit there it would be better.

I am happy to say I am using Method #3.

[pianotuna]

SJ-Chris wrote:


I believe all the batteries are about 14 months old. To me, that makes them relatively newish. Assuming they are all in good health, I'm willing to add a 3rd battery which is brand new (same manufacturer/size/etc).

-Chris

Please at least wire the new batteries in a balanced manner. Method #3 is the only way to do so for odd numbers of jars.

http://www.smartgauge.co.uk/batt_con.html

I suggest adding some plywood to the compartment you are going to use--and if all 3 batteries will fit there it would be better.

[SJ-Chris]

jdc1 wrote:

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.

I believe all the batteries are about 14 months old. To me, that makes them relatively newish. Assuming they are all in good health, I'm willing to add a 3rd battery which is brand new (same manufacturer/size/etc). If this new battery ends up eventually dying 14 months earlier than it would have normally because one of my existing batteries goes bad and takes the other two with it, I'm okay with that. When that time comes, if I still even own this RV, I'll replace all 3 batteries at that time. I've been having pretty good luck buying Group 29s (RV/Marine Deep Cycle) batteries from Walmart usually for ~$90 each which to me seems pretty cheap.

I believe the "only put batteries of the same age" mantra is really trying to protect people against a scenario where you might, for example, have one very old battery that is about to die. If you add in parallel a 2nd brand new battery in that scenario, it is likely that the bad battery will very quickly kill the good battery and then you pretty much just wasted money on that new battery.

-Chris

[SJ-Chris]

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

[SJ-Chris]

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]

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