First of all, let me introduce myself. I'm Jeff from NW Wisconsin and West Central Georgia.Yep, a snowbird. I make at least 2 trips per year and camp on and off the rest of the year. I "tented" until I got old enough to need a little comfort. Owned 3 different "campers" in the past several years from a 1967 converted Chevy school bus to a class A Winnebago (for sale). I now have a 2006 Roadmaster Toy Hauler. I am in the process of upgrading to my needs. Now to the "meat" of this post.This topic has probably been talked to death, but I really cannot find an answer. I have installed a 3000 watt (6000 peak) inverter and a power transfer switch. I have on order 400 watts of solar power and a WindyNation P30L Charge Controller. I have moved the batteries to the inside storage and I have room for four (4) batteries. I need some insight, pros and cons and input on should I have four 12 volt deep cycle batteries in parallel or four 6 volt batteries in a combination of series and parallel to produce 12 volts?

Since you put the batteries inside, you should only use AGM or lithium ion batteries. You should use 6 volt batteries.

I vote for four 6 volt batteries but the Trojan T1275 12 volt has 150 amp hours and two of them may be my next choice. As said above wet cell batteries can’t be inside for safety.

Since you intend to run a large inverter, cell count matters. Four 12 volt batteries may exhibit far less voltage drop than four 6 volt jars.12 volt AGM was my choice--but I do not store them in the living quarters.I've measured loads of 280 amps. It will be important to wire the bank in a balanced manner. Be sure to use the largest wire size that will fit the terminals on the inverter.You don't mention the make or model of the inverter.

WI_Jeff wrote:I have installed a 3000 watt (6000 peak) inverter and a power transfer switch.It's a good idea to consider 24 or 48v inverters for large loads.

If your intending to draw more than around 1000W (80+ amps) on a regular basis, then a bank of 12V wired in parallel will likely be a better choice than a bank of 6V.Why?1) 12V have much lower internal resistance so less voltage drop under high load conditions.2) you will have more batteries in parallel to share the load, so for example when drawing 100A from a pair of 6V EACH much supply 100A, while a bank of two 12V each must supply only 50A along with much lower internal resistance. Going with 4 12V against 4 6V drops the 12V draw to 25A the 6V to 50A.My experience is that nearing 1000W inverter draw you need four 6V to be able to run the load at below 80% SOC.Trojan will give a much similar recomendation. 6V wins with lower current draw along with a much longer cycle life and deeper discharge limits (25% SOC), while 12V wins with high draw but sacrifices some in cycle life and less discharge limit (50%SOC)

6 or 12 volt batteries on towed unit | Good Sam Community

WI_Jeff
Explorer
Jul 09, 2019
Harbor Freight Battery???? Has anyone ever tried the Harbor Freight "Thunderbolt Magnum Solar 12 Volt, 35 Amp Hour Sealed Lead Acid Battery" (Item # 64102). The specs are right with the VMAXTANKS VMAX V35-857 battery (one of the rvweb;s top 10). Price is great at $70 (56 bucks with the coupon) compared to $109. I know Harbor Freight does not make there own batteries. I checked around and cannot find out who manufactures HF batteries. It is almost worth trying 4 of these batteries just because of the price.
WI_Jeff
Explorer
Jul 09, 2019
MORE INFO: The inverter is a "3000 Watt Reliable Pure Sine Wave Power Inverter". I used #2 wire and the longest run is about 40 inches. I will be storing the batteries in the pass-through storage (under the bed)) inside Rubbermaid storage bins with 8 (eight) 2 inch air holes. Reading through your posts I am leaning toward using 4 (four) Interstate (model DCM0035) AGM Deep Cycle Batteries or 4 (four) of the Odyssey PC680 Batteries and running them parallel. I am kind of stuck with 12 volt. THANKS AGAIN for any advice and input. Any other ideas let me know. I am always willing to learn.
theoldwizard1
Explorer II
Jul 03, 2019
IMHO, TRUE 12V deep discharge batteries are almost a scarce as hen's teeth ! Most are "dual purpose" marine batteries which are basically starting batteries with a different label. (TRUE 12V deep cycle battery - Trojan T-1275 Also available in AGM.)

I would go with the four 6V golf cart batteries. Likely to cost less and last longer. AGM batteries raise the cost a lot. If your compartment has ventilation to the outside and is reasonably well sealed from the interior I think you are okay.
pianotuna
Nomad III
Jul 03, 2019
2oldman raises a good point. High wattage inverters mated to 48 volts is a better "fix".

If I were able to start over I'd definitely jump to 48 volts.

Alas it is, for me, a case of champagne tastes but a beer budget.
2oldman
Explorer II
Jul 03, 2019
ktmrfs wrote:
If you're intending to draw more than around 1000W (80+ amps) on a regular basis, then a bank of 12V wired in parallel will likely be a better choice than a bank of 6V.
Higher voltage might work too. Yes, then you need a DC/DC converter for the house.
ktmrfs
Explorer II
Jul 03, 2019
If your intending to draw more than around 1000W (80+ amps) on a regular basis, then a bank of 12V wired in parallel will likely be a better choice than a bank of 6V.

Why?
1) 12V have much lower internal resistance so less voltage drop under high load conditions.
2) you will have more batteries in parallel to share the load, so for example when drawing 100A from a pair of 6V EACH much supply 100A, while a bank of two 12V each must supply only 50A along with much lower internal resistance. Going with 4 12V against 4 6V drops the 12V draw to 25A the 6V to 50A.

My experience is that nearing 1000W inverter draw you need four 6V to be able to run the load at below 80% SOC.

Trojan will give a much similar recomendation. 6V wins with lower current draw along with a much longer cycle life and deeper discharge limits (25% SOC), while 12V wins with high draw but sacrifices some in cycle life and less discharge limit (50%SOC)
2oldman
Explorer II
Jul 03, 2019
WI_Jeff wrote:
I have installed a 3000 watt (6000 peak) inverter and a power transfer switch.
It's a good idea to consider 24 or 48v inverters for large loads.
pianotuna
Nomad III
Jul 03, 2019
Since you intend to run a large inverter, cell count matters. Four 12 volt batteries may exhibit far less voltage drop than four 6 volt jars.

12 volt AGM was my choice--but I do not store them in the living quarters.

I've measured loads of 280 amps. It will be important to wire the bank in a balanced manner. Be sure to use the largest wire size that will fit the terminals on the inverter.

You don't mention the make or model of the inverter.
Lwiddis
Explorer II
Jul 03, 2019
I vote for four 6 volt batteries but the Trojan T1275 12 volt has 150 amp hours and two of them may be my next choice. As said above wet cell batteries can’t be inside for safety.
DownTheAvenue
Explorer
Jul 03, 2019
Since you put the batteries inside, you should only use AGM or lithium ion batteries. You should use 6 volt batteries.

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