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
Aug 07, 2019
Well, what I decided is 12 volt batteries. Got everything going... almost. I have to put the finishing touches on a little bit of stuff. If I can ever figure put how to attach a PDF, I will post my wiring diagram for the batteries and solar power. I want to thank you all for your help.
pianotuna
Nomad III
Jul 11, 2019
Is this the battery you wish to use?

There is an approximate way to get amp-hours from reserve capacity.

In this case, it works out to about 85 amp-hours. But since only 20% should be used, from a Marine "deep cycle", that means only 17 amp-hours capacity per battery. With 4 wired in a balanced manner that suggests a total usable capacity of only 68 amp-hour.

To put this in perspective, my coffee maker uses about 6 amp-hours to brew one pot. The fridge, with a 2:3 duty cycle, running on 120 volts would consume about 21 amp-hours in one hour.

I'm not saying you can't use Marine jars. I did that successfully for over 9 years. But I had 875 amp-hours of batteries in two banks and a modest solar charging system to maintain them.
pianotuna
Nomad III
Jul 11, 2019
Jeff,

It is a bit unusual for deep cycle batteries to have cold cranking amps listed. Is there at least a reserve capacity number? Marine jars do list CCA but depth of discharge is best kept to only 20%. "Real" deep cycle can do 50%.

Please explain what #2 battery cable is. (diameter?)

00 wire has an outside diameter of stranded copper at 0.450 inches and it may be too thin for a 3000 watt inverter.
WI_Jeff
Explorer
Jul 11, 2019
AS for "Do mean #2 or do you mean 00?". I used #2 Battery cable. (The inverter came with #8 wire to use.) As for the batteries, they say on them that they are "deep cycle" and the description sure "implies" that they are. They also have batteries tat are labeled as starting and deep cycle/starting. I know you can't believe everything you read but, I hope if a national company states that their product is a "deep cycle" it is.
pianotuna
Nomad III
Jul 11, 2019
Do mean #2 or do you mean 00?

#2 at 280 amps makes a pretty good fuse.

Even 00 is on the light side for a 3000 watt inverter.

WI_Jeff wrote:
I used #2 wire and the longest run is about 40 inches.
wanderingbob
Explorer II
Jul 10, 2019
Just curious , what will you be running that will require 3,000 watts ?
BarneyS
Explorer III
Jul 10, 2019
This ^^^^^

It has always been my understanding that if a battery had CCA ratings then it was a starting battery and not a "deep cycle". I think that stands for "Cold Cranking Amps" which you wouldn't have on a deep cycle battery since they are not designed for starting use.

I also believe that the deep cycle type batteries have thicker and heavier lead plates and are designed to give out lower levels of electricity over a long period of time and can be discharged lower than the starting batteries. I think the starting batteries have more plates which are thinner and are designed to give out bursts of high energy for short periods of time but will probably have a shorter life due to the thinner lead plates and cannot be discharged as far before damaging the battery.

This is just my understanding of how things work in the battery world. I am not an engineer or electrical wizard so please take my words with a grain of salt. :B
Barney
pianotuna
Nomad III
Jul 10, 2019
What makes you believe they are deep cycle batteries? Nothing in your post suggests they are.

WI_Jeff wrote:
I'm still learning. I'm getting coupons for 20 to 25 percent off on AutoCraft batteries. They have a few that seem to be "true" deep cycle batteries. They are showing from 550 to 675 CCA and a price from $75 each to $88 each. I cannot find the hour rating. If I get 4 (four) batteries, that is not a bad price. I am a little worried about these being "wet" cell batteries and not AGM type. Thoughts? Ideas? Suggestions?
WI_Jeff
Explorer
Jul 10, 2019
I'm still learning. I'm getting coupons for 20 to 25 percent off on AutoCraft batteries. They have a few that seem to be "true" deep cycle batteries. They are showing from 550 to 675 CCA and a price from $75 each to $88 each. I cannot find the hour rating. If I get 4 (four) batteries, that is not a bad price. I am a little worried about these being "wet" cell batteries and not AGM type. Thoughts? Ideas? Suggestions?
DrewE
Explorer II
Jul 09, 2019
35 Ah is a tiny battery, think riding lawn mower or maybe motorcycle size.