Adding a second battery?

[Tiggs]

My new to me TT has a 12V Interstate deep cycle marine/rv battery, spm-24. Looked on line and it offers 140 min. at 25A and it looks like I'm could use as much as 10 amps an hour without the furnace when dry camping, which is what I mostly do. This is probably why my battery is dead in the morning so I want to add a second battery. I would like to add a bigger battery, offering more amp hours but not sure if I have to pair the battery with a similar sized one or if I should replace this battery and convert to a 6V system.

I would like to get to the point where I have enough power at night to run my frig, a light or two, the furnace and the TV for a few hours. Many folks seem to be happier with their 6V power set up over the 12V, but not sure exactly why this is so.

Wonder if I shouldn't go to a 6 Volt system for the general house service and isolate the 12V battery, put it on an inverter and use it only for the TV, thinking if I over did the TV use, I wouldn't compromise my power for the "necessities".

Thoughts?

Carolyn

[CincyGus]

I dumped the group 24 12v battery that came with mine and put two Trojan T-1275 12v deep cycles on the tongue of my trailer. I have an inverter that runs a 11CF residential frig so the extra AH will be a huge benefit and allow me to not have to run the genny daily like I would have had to with the group 24. They also have the benefit of being the same batteries I run in my 48v golf cart and were all bought and installed at the same time. I don't plan on moving them around but if there is a problem, I have the option if I have to.

[Grit_dog]

Double 12v will keep you going for a whole day if you can put a good charge on them daily. Don’t use the fridge on AC. Far more power efficient and cheap to run on propane.
A pair of good 6v golf cart type batteries will give you around double the reserve of 2 normal 12v and aside from the purchase price, are a snap to wire up and no other modifications necessary.

[Atlee]

Biggest problem with 2 12V batteries in parallel is it's hard to find true deep cycle 12V batteries. And they are much more expensive than a 6V golf cart battery.

The so called "deep cycle" battery the dealer puts in a trailer (usually a Group 24) is not a true deep cycle battery.
It's a hybrid or marine deep cycle battery. It combines some of the attributes of a deep cycle battery with some of the attributes of a starter battery.

That's why I pulled the 12V Group 24 battery in my trailer and replaced it with a pair of GC 6V batteries which are true deep cycle batteries.

Tiggs wrote:
I do understand 12v = two 6 volts wired in series. I do get it. I've already done some wiring to power the 12V exhaust fan I installed in the roof of my conversion van doing just that. I've also run 12 power to various points to power other 12V aux. fans when I must leave the dogs in the van without the motor running. I've also replaced the TV with a microwave and wired the van for 120 amp service to it and 4 plugs so I do understand enough to get by.

What I'm trying to decide is if I would be better off to go with two 12 volts wired in parallel or two 6 volts wired in series. I was hoping for an explanation of why, as Matt has touched on, the 6 volt batteries are a better choice. Economically, it would seem to be adding a second 12V would have been the better choice short term, but long term I think, as Matt suggested, 6 volt golf cart batteries or similiar are the way to go.

Carolyn

[Sillybugs2]

Our two batteries that came with tt do fine if we charge 2 hours with gennie on ecomode. Never get below 1/2 usuallyy more beforewe charge tt and electric boat motor jWe have led lights and use tt when dry camping like a tent except fridge. Went 10 days last week all good.kk

[JaneSiver]

bikendan wrote:

thehippie wrote:
Two batteries needs to be at the same age. But what if the first battery is only about two weeks older and you want to
Add a 2nd battery to parallel? Is 2 weeks ok or not at all?

if it's the same battery, brand and model, then you should be fine.

Yes,i personally testing it week ago,you definitely should be fine with that.Just get same models,not necessarily a brand!
I was test batteries for my hair dryer and rest of stuff.

[jplante4]

We put four Interstate GC2s in the Sahara and I also added another 100 watts of solar for a total of 200 watts. I could use another 200 watts of solar, but maybe next year.

The idea was to not be forced into expensive FHU campgrounds for every stop on our next trip which will be 3 months out west. The 4 RV/marine "deep cycle" batteries I replace were shot and wouldn't even last the night if the furnace was on. With my new setup, we can go 3 days without hookups, running the generator once or twice for a couple of hours (mostly for the hair dryer 🙂 ).

[JimK-NY]

Tiggs wrote:
I just picked up two 6V CG2 Duracell Golf Car batteries at Sam's club.....

This battery is rated at 215 AH at 6 volts. That is equivalent to 108 AH at 12 volts. So for two batteries you have 215 AH at 12 volts. If you discharge to 50 percent, you can use 108 AH.

You mentioned pulling 10 amps for a TV and other uses. That will give you about 10 hours of use.

You mentioned draining your previous battery a couple of times and thought that was no big deal. I would recommend you never drain your batteries. Draining batteries even once seems to greatly shorten battery life. You need to monitor battery bank voltage during use. If you are pulling 10 amps you can drop the volts down to about 12.0. With no load you can drop to about 12.2. I would not go lower on a routine basis.

[thehippie]

bikendan wrote:

thehippie wrote:
Two batteries needs to be at the same age. But what if the first battery is only about two weeks older and you want to
Add a 2nd battery to parallel? Is 2 weeks ok or not at all?

if it's the same battery, brand and model, then you should be fine.

yeah everything the same except 2 weeks apart

[bikendan]

thehippie wrote:
Two batteries needs to be at the same age. But what if the first battery is only about two weeks older and you want to
Add a 2nd battery to parallel? Is 2 weeks ok or not at all?

if it's the same battery, brand and model, then you should be fine.

[thehippie]

PapPappy wrote:
I think you misunderstand what a 6-volt system is.....it's two 6-volt batteries that are wired in Series, to create 12VDC. Because of the larger size plates and such in the 6-V battery, you will get a longer life from it, but you could also just wire two 12V batteries in Parallel, which would double your service life from them.

Try to keep the batteries about the same size and age....or the smaller, older (weaker) battery will drain down, and be useless.

Depending on the age of the 12V battery you have, and if you could use it for something else, I'd probably go for a pair of 6V batteries in it's place.

But, there are also some folks, who feel that you should stick with 12V batteries, because, if you have a failure of one of those 6V batteries, you are out of business....at least with just one 12V battery, you can still limp home, or stay another day!:)

Read up on how batteries can be wired together....parallel vs. Series, so that you understand the operation before you do anything....or ask a friend who knows these things, to help you.

On edit, I guess we were typing at the same time:)
Anyway, if you have the 6V batteries, you don't have to worry about your inverter...you would just wire it up to the both batteries to get the 12VDC connection from them (with batteries wired in Series).
Hope that helps.

In your current situation, I'd just get another 12V battery that is the same size as what you currently have, and wire it in parallel.:)

Good Luck:)

Two batteries needs to be at the same age. But what if the first battery is only about two weeks older and you want to
Add a 2nd battery to parallel? Is 2 weeks ok or not at all?

[BarneyS]

Tiggs wrote:
I just picked up two 6V CG2 Duracell Golf Car batteries at Sam's club. They were $89 plus tax. I did have to pay a $15 core charge for each battery but I can bring in two old batteries and get the core charge back.

Now I need a battery box or boxes to fit on the tongue 😉

Battery box for GC2 batteries

Another one.

Another one.
Barney

[Tiggs]

I just picked up two 6V CG2 Duracell Golf Car batteries at Sam's club. They were $89 plus tax. I did have to pay a $15 core charge for each battery but I can bring in two old batteries and get the core charge back.

Now I need a battery box or boxes to fit on the tongue 😉

[MrJoelieC]

This Topic is extremely helpful thanks for the same question I had and the good responses!

I think that since I will probably not Boondock for more than a long weekend I think 2 12 volts are in my future. Mostly based on Price and availability.

For now I will see how the single 12 volt does and if needed I can quickly turn the truck around and throw a charge on until I can get a 120 watt Solar.. I have the LED lights on order already so hopefully that will help..

[wintersun]

I would consider 6v batteries if I had space for four of them. With two 6v batteries if one cell fails the entire battery setup is compromised. Not a big deal with a golf cart or electric forklift where replacing a battery at the shop is no big deal but not something I want to worry about in the boonies.

Less than 12v batteries are done to minimize weight. Two 60 lb. batteries are easier to manage than a single 120 lb. 12v battery with the same AH capacity overall. Batteries are also available in 4v and 2v types.

If you have a flooded lead acid battery already and want to add a second battery it should also be this type and not an AGM or gel type of battery. Flooded lead acid type work best in normal RV situations where batteries may not be fully recharged after each use. Their primary shortcoming is less power in temperatures under 40 degrees where AGM batteries function much better.

Flooded type are going to be the cheapest to own over time so if you have the room and the space is properly vented and you don't mind periodically checking the fluid levels in the cells and adding distilled water from time to time then these are the ones to get.

A first step though should be to add an accurate charge metering device like the one from TriMetric. I would not rely on the RV manufacturer's meter to provide an accurate picture.