AGM Battery Selection

grassgd

My Interstate wet cell battery needed replacement, so I bit the bullet and moved the battery location under the drivers side compartment housing the electrical WFCO and installed an older 50 aH Optima battery I already had along with a new Victron BMV-712.  Now everything is working I need to get a new larger AGM battery.  I can only fit one Group 31 size battery so looking to get highest amp hour rating that I can fit which appears to be from 100 to 135 amp hours. 

Here are two of the Group 31 batteries I am considering:

 

Mfg	Model	20 hr amp-hrs	Weight	ah/lb	$/ah
NPP	NP12-100Ah	100	67	1.49	1.9
VMAX	XTR31-135	135	74.8	1.80	2.4

I would like to get the 135 amp-hr one but can a battery with only 12% more weight really provide 35% more capacity or is this just marketing hype?  I assume in reality battery capacity must be related to the amount of lead used hence battery weight.  

Grumpy_G

A quick Google search shows that there are basically no group 31 135 Ah batteries, combined with the flashy marketing I'd say VMAX is all hype. If you look closely at the cases of group 31 AGM batteries, they appear very similar, lots of rebadging in this industry. 

pthomas745

Usually, the group size would correlate with the number of amp hours.  The difference in amp hours is easy to see between a group 24 battery  of 85 ah (10.2"*6.5"*8.2"h) and a Group 30 of 100 ah. (12.17 x 6.61 x 9.16).

The group 24 measurement above is from the Vmax Group 24 battery.  Compared to other Group 24's, it seems that Vmax..quotes higher AH ratings than the other batteries on an Amazon search for "Group 24" battery.  All the others seemed to come in around 75-80......so, Grumpy's comment about hype would seem to be accurate.  (Many owners here have the Vmax dual 6v, in any case).

There are lots of batteries in the 100ah AGM space that would work.  I had this one in my Amazon wish list before I was lured away by a 400 dollar 100 ah lithium. 

https://www.amazon.com/Universal-Power-Group-100Ah-Battery/dp/B00S1RT58C

The lithium batteries have dropped in price in the last couple of months.  If you can work out the "low temperature charging protection" issue, you can get a 100 ah lithium battery for less than 400 dollars.  This would basically be 90 usable amp hours.  I have one of these types of batteries, (AmpereTime), have set up my solar controller with a temperature sensor, and it has worked very nicely.  (The other low temp protector is...me).

This Chins battery gets great Will Prowse reviews.  The "smart" version of the battery below has the low temp protection, and is usually sold out.....

https://www.amazon.com/CHINS-Rechargeable-Parallel-Road-Trip-Wireless/dp/B09F9M82VN/ref=sr_1_3?keywords=CHINS&qid=1666176295&qu=eyJxc2MiOiIzLjY5IiwicXNhIjoiMy4yNCIsInFzcCI6IjIuODEifQ==&sr=8-3&th=1

bergger

I would seriously consider Trojan batteries for AGM.  I've have them in the past and they are probably the best AGM battery you can buy.  Built to deal with shock and vibration and work well in extreme low temps.  Plus they are manufactured in the USA.  Long lasting and well worth the money in my opinion. 

https://www.trojanbattery.com/motive-agm/

seabear31

I think bergger is right to suggest Trojan brand batteries.  I use twoTrojan T-105 wet cell golf cart batteries which I think are excellent. 

Horigan

@grassgd, In case you're not already aware, realize that you need to add a venting system to an AGM or lead acid battery if it's installed inside the trailer.  These batteries can produce hydrogen gas during faulty charging that needs to be vented outside.  This would involve an enclosure and vent tubing to the outside.  Lithium batteries do not require this.

grassgd

Horigan said:

@grassgd, In case you're not already aware, realize that you need to add a venting system to an AGM or lead acid battery if it's installed inside the trailer.  These batteries can produce hydrogen gas during faulty charging that needs to be vented outside.  This would involve an enclosure and vent tubing to the outside.  Lithium batteries do not require this.

Thanks,  I plan to vent the battery box as you suggest if I stay with an AGM battery.   I should consider switching to Lthium at this point first.  Only hold back is my current solar panel controller will not work with Lithium and would also need to be changed along with the WFCO battery charger.

I have never felt very confident in the WFCO charger since I can never tell if it actually performs a charge above about 13.6 volts.  I saw where you can replace the charger section of the WFCO with another battery charger, but I don't think that option covered Lithium battery charging.  Not sure how to keep the WFCO for house 12 volt power supply and use a separate dedicated charger for either new AGM or Lithium battery.

bergger

You'll probably need to upgrade the converter box as well to support lithium.  

grassgd

bergger said:

I would seriously consider Trojan batteries for AGM.  I've have them in the past and they are probably the best AGM battery you can buy.  Built to deal with shock and vibration and work well in extreme low temps.  Plus they are manufactured in the USA.  Long lasting and well worth the money in my opinion. 

https://www.trojanbattery.com/motive-agm/

I like looking for USA manufactures although they usually come at a price.  X2Power is another USA AGM battery that I looked at that comes with a 48 month replacement.  Their Group 31 AGM is rated at 103 amp hours and weighs 75 lbs.

grassgd

bergger said:

You'll probably need to upgrade the converter box as well to support lithium.  

This was on my to do list even if I choose the AGM battery since I don't think the WFCO is the best charger to maintain flooded batteries or AGM's.  My Optima battery charger I use on my vehicles includes a special conditioning algorithm to extend the battery life I think. 

CharlieRN

The WFCO on my 2021 is not capable of fully charging my LFP batteries either. That's only an occasional issue, as the batteries don't need to get 100% every time. I'm not sure this is the case for all lithium batteries, but the BB's only need to be topped up once a month or so to properly balance the cells. My work-around is to plug in my Victron AC charger occasionally. The Victron comes with harness that can remain connected to the batteries, so connecting is easy as you can see in the photo below.

grassgd

CharlieRN said:

The WFCO on my 2021 is not capable of fully charging my LFP batteries either. That's only an occasional issue, as the batteries don't need to get 100% every time. I'm not sure this is the case for all lithium batteries, but the BB's only need to be topped up once a month or so to properly balance the cells. My work-around is to plug in my Victron AC charger occasionally. The Victron comes with harness that can remain connected to the batteries, so connecting is easy as you can see in the photo below.

The other downside is while towing, I don't think the power from the tow vehicle alternator is capable of completely charging the lithium batteries either, hence the batteries will be slightly under charged until you use 120 volt power with a proper lithium battery charger.

I was thinking of making a change from using the WFCO charger anyway.  If and when I do, I will make sure I get a charger that can handle any type of battery.  If I use an AGM battery now, I can live with the WFCO and supplement it with my Optima battery charger like you do with your Victron charger and don't have to change out my solar panel controller.  

bergger

To really get a full charge on lithium batteries while towing you need a DC to DC charger added.  Otherwise most vehicles can only charge lithium up to about 80%.