connecting two 12 volt batteries in tandem

[woodman]

I'd like to have two RV batteries for over night to handle the furnace and a few other small essentials. Our RV came with one and I was thinking adding a second deep cycle 12V battery. Basically, I believe one connects the positive to positive and negative to negative, however; the lead battery has the positive to the RV and the second battery has the negative directly connected to the ground thus creating a full circuit. Not sure. Is anyone familiar with the proper wiring to handle two 12V deep cycle batteries?

[bncinwv]

Here is the way:



I will add that I took it a step further and added an isolator switch into the circuit as well. This allows me to use one or the other or both when needed. It also lets me completely isolate the batteries so they do not discharge during winter storage.

Bingo

[HOOK]

Your are right. Had 2 in the last one. Will have 2 in new one soon. But I recommend using both at all times and when one eventually dies, replace both for better success. A weak battery will pull a strong one down.

[bncinwv]

Larry, that is true, unless they are isolated from each other. I typically use one or the other and charge them separately as well. When both are low, I have the capability of selecting both for an amperage bump (for instance, starting the generator), but this circumstance has been very rare. The switch I use is actually made for boats with a house and starting battery, but it works well in the application I am using it. May not be for everyone, but it works for me.
Bingo

[DQDick]

We've used both wired that way for several years. We don't use cutout switches, but it is an interesting idea. The only thing I would add is that I try to match the batteries. That means when I went to two I sold the OEM battery and went with two of the best Interstate Deep Cycle Batteries I could buy.

[NCFischers]

I've done the same thing as Bingo. With the isolater switch, I can have control over usage if I want to.

[mazboy]

always use the same amp rating on both batteries. if you don't it is the lowest amp rating you will get.

[deadeye]

I done the same as Bingo on the setup, but went a step farther on more expensive Gel batteries. You can use either one or both as needed. My reasoning for the Gel batteries was that you never have to add water to them. Here is what I used and I didn't go with the cheapest one. There are (11) different ones to choose from for whatever your needs are. I might add that I am not affiliated with this company at all, but batteries of this kind last as long as 10 to 12 years. I think I used the size group 31...JB

http://www.remybattery.com/Deka-Inti...Batteries.aspx

[Flymutt]

Don't forget to get a larger battery box...they still need to be vented, unless you get AGM batteries

[timandsusan]

I installed a 2nd 12V battery connected as shown. For the vent--I used PVC pipe joints and swimming pool vacuum hose to connect the second battery to the existing vent hose. Easy to get at any hardware store--used screws to hold it together--works great.