Second battery

Hard to give a good answer without more information.
If the "old" battery is more than 3 years old and/or has been run WAY down more than once, I think it should be replaced too.

No need to separate two batteries into "banks" unless one is a LOT bigger than the other. Two the same in parallel is the most common arrangement in a situation like yours. Unless you got real fancy with the cables, the added one will tend to discharge and recharge slower because of the cable lengths.

From my experience batteries of different age might mess each other only if left connected in storage for long time.
When you constantly use/recharge the batteries, you always use both regardless minimal differences in voltage.
I run dual batteries in several vehicles and even batteries bought together, having the same manufacture date can show 0.1V difference.
In my boating years I had my travel trailer in storage close to the lake.
With no hookups, I was taking trailer battery home for recharging, but for emergency brakes and short run of water pump I put old motorcycle battery in it.
The recharged big battery would connect with alligator clips to much smaller and much older battery and work whole weekend just fine.

Everyone has always told me that the batteries should be the same age. However, I think you have another issue because they are some distance apart. I think I would consider another switch and charge them separately and run them separately as well.

I don't know why you are needing the second battery, but if you haven't switched to LEDs, you probably should.

Finally, I'd measure the compartment and potential batteries. All Group 24, 27s, etc aren't exactly the same size and they also are different amp rated as well.

My Lance had a compartment for one battery. The first battery was an Optima, I went through three of those over a three year period. They just went bad. I put in a group 31 AGM in year four, I think. Then I added a second battery under the wing of the TC. I used 8ft of marine gauge no 4 cable with an Anderson connection. I ran this set up for about six year without a problem. Last year the older battery went bad so I bought two new ones.
The point being the battery's were not the same age nor manufacture and I got good service from my set up.

jimh425 wrote:
Everyone has always told me that the batteries should be the same age. .

They also tell you to not put 2 different oils into your engine and not to mix vodka with beer.
But to give more explanation to what I wrote above.
Let's say you have one battery that fully charged has 12.5V and you hook up parallel with other one that has 12.4v
If you leave them like that, the lower battery will drain the power from the higher battery.
But in RV, you hook them up and almost immediately start using, so after some time they both will discharge to 12.3v for example.
At this point the difference doesn't matter.

Kayteg1 wrote:

jimh425 wrote:
Everyone has always told me that the batteries should be the same age. .

... not to mix vodka with beer.

Isn't this how they make light beer? :B

Wayne

Our experience is that two batteries are a real good idea. You can run the systems in the camper without wondering if there is enough power for the furnace.

I would just parallel them and not put in a switch. If your present battery is serving you well, just get another series 24 and see how it goes. Also, I have had amazing results with batteries from junk yards, takeouts. I use them for miscellaneous purposes and they last, years. For $15-$20 its worth a try. I know, I know they are not supposed to be as good as new batteries, they are not, but the two that I have around I have had for 4 years and will not die. (Better then my last set of 6v from Costco.)

Rick

Kayteg1 wrote:

jimh425 wrote:
Everyone has always told me that the batteries should be the same age. .

They also tell you to not put 2 different oils into your engine and not to mix vodka with beer.

Now that we've established you mix vodka with beer and mix two oils for your engines, the full quote is below.

"Everyone has always told me that the batteries should be the same age. However, I think you have another issue because they are some distance apart. I think I would consider another switch and charge them separately and run them separately as well."

By now, you should know better about taking quotes out of context. I suggest you should allow other people's comments to stand on their own. If you want to revise your comments, go for it.

No need to take offense. Just a bit of humor to point out we are told lots of things that may or may not be true.

I have read many times that the batteries should be the same age. My logic says this is true, but then it is based on theory and gossip, not personal experience or education. I will mix oil and have been known to mix Vodka with beer.

Wayne

I added a second battery (in a box) in the wheel well that plugs into the side of the camper and wired into the main battery box. I added a switch that allows Bat 1, Bat 2, Bat 1 + Bat 2 & off. wasn't very expensive off eBay and now I have all options. My batteries are currently mismatched so I run one at a time. I may not even switch to parallel when I eventually get matched batteries since switching batteries gives me a good indication when I have used roughly half my power. I usually run off the old weaker battery first. When I'm on the road and plugged in every night I switch between the batteries every few days just to keep them both topped off. Same time I put in the battery switch I added a meter beside the switch so I could quickly decide if I needed to switch batteries.