AGM Deep Cycle Battery suggestions

[Jimmygator]

I'm needing to replace my TT battery. It historically had the flooded 24 group size deep cycle RV/Marine type battery. While doing light research, and not trying to break the bank, I'm interested to know how to choose the better fit battery. I do some off grid trips however few. I generally carry a generator and have a 110 watt solar panel when off grid.

One that has my attention is VMAX V35-857 AGM Deep Cycle Battery. I have no idea what this battery's typical application is and unsure if it should be used in a TT.

Any other ideas are absolutely welcomed.

TIA

[sundancer 87]

Battery questions are always good for lots of suggestions.
If you think you want a deep cycle battery to go along with your solar panel then get a true deep cycle battery.
True deep cycle batteries are rated in Ah, not CCA nor CC nor marine ( never learned how a battery knew is was a marine application), or any other hype words used to sell a battery.
Visit solar stores and check out their battery selections for real applications. Most solar providers have extensive explanations regarding the components of solar systems.


https://www.solar-electric.com/marin...ttery_type=443 True deep cycle batteries are sold here as an example.

[persistent]

I have Interstate Marine AGM batteries. Each of the two are 100 amp hour group 31. If you choose a group 31 you will probably need a bigger battery box. The boxes are cheap on Amazon.com or at Etrailer.com. They are 4 years old and work just like new. I always fully charge them before storage. No other maintenance needed.

If you want a "better" battery for occasional off-grid use, marine AGM is a good choice. "Better" is just my opinion.

On the other hand deep draw flooded cell batteries are cheaper. If you want only one battery it will have to be 12 volts, not 6 volt gulf cart batteries. Still be sure it is deep draw design.

Choosing An RV Battery https://www.irv2.com/forums/download...do=file&id=231
This is a good article, but its recommendations against “Marine Batteries” does not apply to “Marine AGM batteries”.

[chily3]

I use 2 6 volt golf cart batteries. They last longer on a charge

[dsol]

I upgraded to two group 27 from two group 24 batteries. The only difference in size is length as height and width are identical—or at least should be.

My new batteries fit (barely) in my existing battery boxes. I went with sealed AGM deep cycle that were branded as Duracell. The advantage of AGM is they supposedly do better with vibration and can be mounted in any direction although that probably doesn’t matter 99% of the time.

The main reason I went with these is I found them in stock at a battery retailer during the height of the pandemic but I have been happy with them so all in all a good purchase. About $220 a piece so not cheap but less than the best ones.

[lcv800]

Funny, I just went the same route with the same batteries. Time will tell if we made a good investment.
Rusty

[wfburton159]

The only potential trouble with AGM is that they do not like to be discharged. If they are often discharged they will not last. If you are constantly charging them they are good batteries, but if they go dead they will be shot.

[Eric H.]

Originally Posted by Jimmygator

I'm needing to replace my TT battery. It historically had the flooded 24 group size deep cycle RV/Marine type battery. While doing light research, and not trying to break the bank, I'm interested to know how to choose the better fit battery. I do some off grid trips however few. I generally carry a generator and have a 110 watt solar panel when off grid.

One that has my attention is VMAX V35-857 AGM Deep Cycle Battery. I have no idea what this battery's typical application is and unsure if it should be used in a TT.

Any other ideas are absolutely welcomed.

TIA

VMAX Batteries are a very good option in my opinion. I just sold our last TT that had 2 VMAX SLR125 batteries. The batteries were 7 years old and still holding a charge with absolutely zero maintenance. Just 185w solar system to keep them charged at all times and I didn't have a generator for that rig. I never disconnected them and there is no water to check. They also do not need to be vented so they don't have to fit in a battery box which can give you options for mounting locations as well as adding a battery. I mounted 2 in a closet of our first TT. 8 years ago no one had heard of VMAX but I went out on a limb and ordered 2. Now they are very highly rated.

As far as the VMAX you have in mind, that's probably not a good option but only due to capacity. VMAX does lists that battery for RV and Solar applications. Your original flooded battery was likely around 75ah capacity but the VMAX you're looking at is only 35ah. You need to look at at least the 80ah batteries to be at the same capacity you had before or add another battery in parallel to give you 70ah. Figure out how much room you have and then see which VMAX with the highest amp hour capacity will fit in your battery tray. Two 6 volts in series are better than one 12v but two 12v in parallel are better than the two 6v. If you're into dry camping I would definitely find room for two batteries. Or you could triple your capacity with one 100ah lithium because you can use 90% of that 100ah without damage.

[persistent]

Originally Posted by wfburton159

The only potential trouble with AGM is that they do not like to be discharged. If they are often discharged they will not last. If you are constantly charging them they are good batteries, but if they go dead they will be shot.

Why do you say this?
No lead acid battery lasts long if it is stored at a low state of charge, but:
AGM hold a charge disconnected for 12 months.
AGM can be drawn down flat without noticeable loss of capacity or life.

Battery University https://batteryuniversity.com/articles

How does the Lead Acid Battery Work?
https://batteryuniversity.com/articl...d-battery-work

How do battery chargers work
https://batteryuniversity.com/articl...-chargers-work

How to Charge and When to Charge?
https://batteryuniversity.com/articl...when-to-charge

[wfburton159]

Originally Posted by persistent

Why do you say this?
No lead acid battery lasts long if it is stored at a low state of charge, but:
AGM hold a charge disconnected for 12 months.
AGM can be drawn down flat without noticeable loss of capacity or life.

This is just my experience with them. They (AGM) seem be killed much easier than a regular battery if not maintained.

[Eric H.]

Originally Posted by persistent

Why do you say this?
No lead acid battery lasts long if it is stored at a low state of charge, but:
AGM hold a charge disconnected for 12 months.
AGM can be drawn down flat without noticeable loss of capacity or life.

I didn't read all that but my personal experience is that AGM's do not tolerate being "drawn down flat". I allowed that to happen with my first pair of group 31 Decka AGM batteries within the first year. I had a 85w solar panel but that wasn't enough to keep the batteries charged in the winter with the parasitic draw from the refrigerator electronics. Luckily I was able to warranty the batteries but I learned my lesson and started pulling the fuse for the refrigerator when storing it in the winter. Later I added another 100w panel and that was enough even with heavy cloud cover to keep the batteries topped up with the fridge fuse in place. That was about 15 years ago and the replacements lasted 8 years. Those were replaced with the VMAX AGMs 7 years ago and I just sold that trailer a few months ago with those batteries still holding a charge.

I'm not sure where you read that AGM's can be drawn down flat but I have experienced the opposite and I've read a whole bunch of AGM threads that say the same thing from first hand experience. They're great batteries and can live 8 years plus if kept charged and not drawn down too far with zero water maintenance.

[wfburton159]

Originally Posted by Eric H.

I didn't read all that but my personal experience is that AGM's do not tolerate being "drawn down flat". I allowed that to happen with my first pair of group 31 Decka AGM batteries within the first year. I had a 85w solar panel but that wasn't enough to keep the batteries charged in the winter with the parasitic draw from the refrigerator electronics. Luckily I was able to warranty the batteries but I learned my lesson and started pulling the fuse for the refrigerator when storing it in the winter. Later I added another 100w panel and that was enough even with heavy cloud cover to keep the batteries topped up with the fridge fuse in place. That was about 15 years ago and the replacements lasted 8 years. Those were replaced with the VMAX AGMs 7 years ago and I just sold that trailer a few months ago with those batteries still holding a charge.

I'm not sure where you read that AGM's can be drawn down flat but I have experienced the opposite and I've read a whole bunch of AGM threads that say the same thing from first hand experience. They're great batteries and can live 8 years plus if kept charged and not drawn down too far with zero water maintenance.

Exactly my point. 100% experience that they will not come back from being drawn down.

[persistent]

If you want to know, there are books and factual websites to read. Here is a good source.

Battery University https://batteryuniversity.com/articles

How does the Lead Acid Battery Work?
https://batteryuniversity.com/articl...d-battery-work

How do battery chargers work
https://batteryuniversity.com/articl...-chargers-work

How to Charge and When to Charge?
https://batteryuniversity.com/articl...when-to-charge

Life is complicated. Sometimes with so much going on we come to faulty conclusions.

The facts are:
All lead acid batteries must be stored fully charged for long service life. It does not matter whether they are flooded cell gulf cart batteries or marine AGM. They all use the same basic lead and sulfuric acid chemistry. They all fail if stored for three months in a discharged state.

They all produce lead sulfate as they discharge. Lead sulfate always crystalizes over time. Crystalized lead sulfate is always hard or impossible to redissolve while charging.

AGM benefits

AGM batteries tend to produce less lead sulfate build up at the bottom of the battery. Long charging time can sometimes redissolve lead sulfate that tends to stay pressed against plates by the Absorbed Glass Mats in AGM batteries. Not so in flooded cells. In flooded cells the crystals tend to fall off the plates as the surrounding sulfate is redissolved.

AGM batteries do less damage to supporting structures when drawn down flat. The acid in AGM batteries is absorbed into glass mats pressed against electrodes. The amount of acid in the pads is limited. The battery runs out of acid before discharge can erode the plates.

AGM weaknesses

Most AGM battery designs are sensitive to high voltage. Charging lead acid batteries produces hydrogen gas. AGM batteries have chemistry that recombines the hydrogen gas with oxygen to produce water.

That process limits the amount of gas that can be recombined. High voltage while charging produces more gas than most AGM's can recombine. They then vent. Venting loss of water is permanent and cannot be replaced. Loss of water in flooded cells is relatively easy to replace.

Many AGM's can manage charging voltage of 14.4 volts for 4 hours or so. Longer than that can cause venting. Lifeline AGM batteries are spec'ed to handle 14.4 volts for longer periods. Most other designs are not.

I wish you good luck and happy trails ahead!