6v series vs 12 v coach batteries

[markopolo]

Imbalance between the individual 2V cells occur whether it's a 6V or 12V battery. Example of 6V battery specific gravity variance: https://forum.solar-electric.com/dis...meter-readings - Example of 12V battery specific gravity variance: https://www.solarpaneltalk.com/forum...048#post397048

6 cell 12V lead acid battery.jpg

I prefer using 12V batteries for 12V lead acid battery systems because between 2V cells #3 & #4, I think that internal cell interconnect on a 12V would be better than the external interconnect (wire, lugs) on a 6V battery.

The heaviest/largest battery or combination of batteries that will fit in the available space will most often have the greatest capacity rating.

Just an opinion, & happy to read any research paper that delves into quantity of cells leading to greater cell variance (max high/max low differences).

[booster]

I think the big difference between 6v and 12v is basic design to purpose as most two battery 12v systems are going to have the same amount of cells.


My preference is two six volt batteries if you get up to the 200ah bank size area as those batteries have been tweaked over decades of of time to maximize deep cycle durability by the manufacturers. This is particularly true of the wet cells, with the top brand like Trojan being very forgiving of abuse. AGMs are probably less different between 6 and 12v, but I haven't seen any data on that to prove it. Lifeline did tell me that their 6 and 12v batteries had essentially identical cells.


As was stated by others, sometimes the packaging size and shape will dictate what will fit the best and will make the decision for you.


If I were choosing wet cells, two 6 volt GC batteries would be my choice as there are almost no real deep cycle 12v wet cells around any more.


For AGM, I would probably not worry about six or 12v with Lifeline and probably a lot of the other brands as long as they were true deep cycle batteries. There are other versions of AGM that aren't suited to RV use like UPS batteries that are more designed for long term float, low cycling rate use. Other AGMs might be pure starting battery design or combo style, with Optima being a good example of that.

[Jon in AZ]

I’m wondering what model Roadtrek this is? Could be wrong, but I thought only the E-trek (lithium) models came with a 12V compressor fridge. I can’t imagine any factory set-up with only a single 12V lead-acid battery powering a compressor fridge.

My ‘14 P190 came with 2@6V GC2 AGMs and a conventional 3-way fridge.

Moving forward, knowing the model and the location and size of the battery compartment will determine what’s possible.

[btripper]

It's a 2016 Simplicity. We bought it used and it only has the one battery. Could you give me more information on your lithium batter?

[Jon in AZ]

No lithium. I have an old school set-up with 6V GC2 (golf cart) lead acid batteries. In hindsight, for my fairly minimal use and power requirements at the current time, a single larger 12V would probably have been enough. But I can run my fridge on propane.

Lithium means changing the charging system as well as the batteries. Very pricey. Don't think that's an option for you.

Your choices are one or two, 12V or 6V, flooded or AGM. Flooded requires an exterior or interior vented battery compartment and access to do periodic maintenance of the water levels. AGM's are usually used when there is restricted access. That's why I asked about the size and location of the battery compartment.

Conventional wisdom for two-battery systems is 6V lasts longer (more cycles) due to larger cells and thicker plates. I'm hearing that may not necessarily be true in all cases. They're heavier and larger than a pair of 12V with the same capacity. Good maintenance is critical with all conventional batteries.

I do think you should investigate carefully what else might be running down your battery overnight. On mine I discovered there were several things running in standby mode when the inverter was on. The inverter switch was opposite the other switches on the panel (and had no indicator light), so it was on when I thought it was off.

[btripper]

Thanks for this. The battery is suspended under the chassis, so AGM would be required. I'm thinking 2 6v if I can. After looking at Lithium, the payback period would be too long. We are only summer users, but are hoping to go across Canada this summer if the virus thing let's up.

[GallenH]

I too don't quite understand this. The specs for a 2016 indicate that the fridge is "electric/propane." Could the previous owners have replaced a 2 or 3-way with a compressor? If that's the case, the single battery capability seems short sighted. Since I've been watching the forum on this topic for a while (I have a 3-way that's functioning but old) I've gotten the impression/advice that 200ah would be a safe capacity to have.

As to your "under the chassis" comment on location. My battery compartment is under the living compartment, vented to the outside and sealed off from the interior by a panel with weatherstripping around it. Clearly (1997) intended for a wet cell. I've since gone AGM but wouldn't have had to given the separation.