Battery Compatability

For what it's worth (probably not much), the design of our Itasca Class C is such that the 2 coach batteries get directly connected to the engine starting battery (all 3 are hooked up in parallel with each other) whenever we're driving. The ignition key automatically switches ON a solenoid that connects these 3 batteries together whenever the engine is running.

The coach batteries are a couple of 12 volt 100 amp hour deep cycle AGM batteries that will be 8 years old this fall. The engine battery is a regular wet cell engine starting battery that is probably around 5 years old.

As far as we can tell on RV trips all 3 batteries are still functioning fine. When camped and in storage, the RV's stock 13.8 volt converter keeps the coach batteries charged. When in storage a small multi-stage BatteryMinder is continuously hooked up to the engine battery. Of course whenever we're on the road, the engine alternator's voltage (varies from as low as around 13 volts in hot weather up to as high as around 14.5 volts in cold weather) gets applied to all 3 batteries.

Our situation seems to show that under certain conditions, AGM deep cycle batteries can be mixed with a wet cell engine starting battery.

I like having the switch easily accessible. I also like having the batteries inside but that's not going to happen.

After reading your post EMD360 I went out and looked at the battery. I don't have any technical data but the battery reads: 24DC 690MCA 101 amp hours @ 1amp-for marine, trolling and RV applications.

At $74.95 with a 2 year replacement warranty its hard to beat it.

Also the Walmart battery is not actually 110 ah. It is more like 73 if I remember right. They rate their batteries in amp minutes not hours and I figured out the conversion after I bought it.

I bought the same Walmart DC battery to replace a dead marine battery. It appears to be a good battery for the money.
I also experimented with two used AGM's and separated them from a different marine battery with a Blue Sea switch. I like the switch because even though the AGM's eventually died, (using an older Magnetek converter that I have not updated) I can disconnect the house battery from inside using the switch. I have toyed with the idea of replacing the AGM's but we are not boondocking as much here in Colorado as in Arizona. Maybe next winter if we take an extended trip.
The nice thing about AGM batteries is that they don't have to be vented and they can be mounted in almost any position.

This dinette bench is directly above the battery compartment. a hole was drilled through the floor and the cables were run through a short piece of pvc pipe. You can see the Blue Sea switch mounted inside too.
I could use all the batteries together if the converter was not running but charge them one type at a time when it was.
I am not sure if the setup killed the AGM's prematurely since they were used when I bought them. But each of them started showing an error code when I tried to charge them with a smart vector charger and no amount of turning them upside down or other tricks worked to get them to charge again.
The switch was not too expensive and allowed me to use both types of batteries independently.

I bought recently bought two 6 volt USA RV batteries for $99 apiece, same as original 6 volt T-105's. Two large capacity 6-volt batteries in series, paired with a good modern converter/charger like the Progressive Dynamics PD9245, are a common Class C 12 volt house battery setup. The battery compartment in our 2004 Tioga 26Q fits two 6-volt batteries.

Cheaper do it right first time.

wolfe10 wrote:
Several reasons not to mix an old and new battery, but a major one is that the old one will kill the new one. Here is how it can work: a cell in the old battery goes bad. Your charger, even a smart one knows to charge at a certain voltage. If it sees voltage is low because of that bad cell, it will keep charging the batteries. This OVER-charges the good battery. That is why battery failure is often accompanied by batteries boiled dry and swollen cases-- severe overcharging.

The reason for not mixing battery technologies is that each has a "preferred" charging algorithm. With a properly programmed smart charger or smart inverter/charger is can be specifically tailored to a battery technology.

This does not mean that you can't mix a new wet cell with new AGM, as their charging algorithms are pretty close, but it is not the ideal setup.

X2 can be done but not the best way to do it you will end up buying more batteries in the long run buy them in pairs and the same cca and brands would be best

Several reasons not to mix an old and new battery, but a major one is that the old one will kill the new one. Here is how it can work: a cell in the old battery goes bad. Your charger, even a smart one knows to charge at a certain voltage. If it sees voltage is low because of that bad cell, it will keep charging the batteries. This OVER-charges the good battery. That is why battery failure is often accompanied by batteries boiled dry and swollen cases-- severe overcharging.

The reason for not mixing battery technologies is that each has a "preferred" charging algorithm. With a properly programmed smart charger or smart inverter/charger is can be specifically tailored to a battery technology.

This does not mean that you can't mix a new wet cell with new AGM, as their charging algorithms are pretty close, but it is not the ideal setup.