6v series vs 12 v coach batteries

[btripper]

we recently purchased a 2016 Roadtrek. The 12v battery will not keep the fridge running all night. It is the original battery and probably has not been well maintained. My question is... would I be better off to replace the 12 v with 2 6V batteries. Any thoughts on this, as well as battery type would be appreciated

[JohnnyFry]

Two 6 volt deep cycle (golf cart) batteries are considered the ideal configuration, betterthan two 12 volt batteries in parallel because the series connection of the 6 volt batteries maintains superior balance of the individual cells. Typically they are 232amp-hour golf cart batteries which give a useable 115 amp hours of 12 volt power at the recommended 50% recommended maximum depth of discharge. Flooded or AGM? Flooded batteries are cheaper and will last several years with care and attention to watering the cells. AGM batteries do not need water and do not emit corrosive fumes but they are more expensive initially and tend to be more easily degraded by misuse.

[eric1514]

Originally Posted by btripper

we recently purchased a 2016 Roadtrek. The 12v battery will not keep the fridge running all night. It is the original battery and probably has not been well maintained. My question is... would I be better off to replace the 12 v with 2 6V batteries. Any thoughts on this, as well as battery type would be appreciated

Is this a compressor fridge? If not, why are you running the fridge on battery all night?

[btripper]

Originally Posted by eric1514

Is this a compressor fridge? If not, why are you running the fridge on battery all night?

its only 12v or 110v, not propane. I'm thinking the batteries should keep it running at least overnight when boondocking

[booster]

Originally Posted by btripper

its only 12v or 110v, not propane. I'm thinking the batteries should keep it running at least overnight when boondocking

Assuming that the battery was full enough at the end of the day, the battery condition was decent, you didn't use a bunch of other power or have inverter on (even if not being used0, the frig is running properly, it should make overnight even on a single battery. Most compressor frigs if in reasonable temps will be using 25-40ah per day with maybe 10ah of that overnight. That is isn't very much, so you do have something else going on. I am assuming you don't have a monitor other than the factory lights.


I think most that have compressor frigs would have the opinion it would be quite difficult if you have a single battery as there is no room for error, or much reserve power there.



You hear on this forum all the time, but it is so very true. If you don't have a shunt based battery monitor, you don't really have a clue or a good way to find out, what condition or state of charge your batteries are in or where your power is actually going.

[btripper]

Originally Posted by booster

Assuming that the battery was full enough at the end of the day, the battery condition was decent, you didn't use a bunch of other power or have inverter on (even if not being used0, the frig is running properly, it should make overnight even on a single battery. Most compressor frigs if in reasonable temps will be using 25-40ah per day with maybe 10ah of that overnight. That is isn't very much, so you do have something else going on. I am assuming you don't have a monitor other than the factory lights.


I think most that have compressor frigs would have the opinion it would be quite difficult if you have a single battery as there is no room for error, or much reserve power there.



You here on this forum all the time, but it is so very true. If you don't have a shunt based battery monitor, you don't really have a clue or a good way to find out, what condition or state of charge your batteries are in or where your power is actually going.

I think it is the battery. it will be 4 years old if it is the original. I'm not electrically savvy, so I'll have to get it tested. Thanks for taking the time to reply

[btripper]

Originally Posted by JohnnyFry

Two 6 volt deep cycle (golf cart) batteries are considered the ideal configuration, betterthan two 12 volt batteries in parallel because the series connection of the 6 volt batteries maintains superior balance of the individual cells. Typically they are 232amp-hour golf cart batteries which give a useable 115 amp hours of 12 volt power at the recommended 50% recommended maximum depth of discharge. Flooded or AGM? Flooded batteries are cheaper and will last several years with care and attention to watering the cells. AGM batteries do not need water and do not emit corrosive fumes but they are more expensive initially and tend to be more easily degraded by misuse.

Thank you fr the information. Great help. Will probably go with the sealed 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).

[avanti]

Another issue with series 6V setups is that if a single cell fails in either battery, you are out of luck. With 12V parallel, you can pull the bad battery and limp along with the other one.

It is not at all clear to me that there is a consensus that 6V setups are considered ideal.

[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.

[GeorgeRa]

Originally Posted by avanti

Another issue with series 6V setups is that if a single cell fails in either battery, you are out of luck. With 12V parallel, you can pull the bad battery and limp along with the other one.

It is not at all clear to me that there is a consensus that 6V setups are considered ideal.

This is indeed a clear benefit of 2 x 12V setup. I am still waiting for a clearly stated benefit of a modern AGM 2 x 6V set-up, it could be ingrained in our DNA.

[btripper]

Interesting point. I'm wondering what the failure rate would be on battery cells, not having any experience with them.

[GeorgeRa]

Originally Posted by btripper

Interesting point. I'm wondering what the failure rate would be on battery cells, not having any experience with them.

I wonder what prompted your question while claiming not having any experience. Same technology lead acid cells are identical in either 3 or 6 cell boxes. Reliability of internal cell connections could be better than external cable. My shot at systems reliabilities:

1- Large 12V battery, likely best, all factory internal connections
2- 2 x 12V battery, if one battery fails you still have a remaining one
3- 2 x 6V, between cable connection failure or one battery failure kill the system

[markopolo]

Looking at Trojan batteries AGM line and calculating kWh/lbs, the 122lb 12V 200Ah J185-AGM just edges out the 6V offerings. That's a heavy battery to handle!


https://www.trojanbattery.com/product/j185-agm/


Very nice to have 200Ah in one case though.

[btripper]

Thanks for the info. Hopefully won't have to handle the batteries too often!