Battery Charging - Is a Disconnect Necessary?

No not at all. Is this rig parked where it gets full sun during the day? If so look into a solar panel, check RV shops and boat shops, especially those catering to sail, and some of the larger truck stops as well. I have one the cell size is 6" by 18" designed to be sewn onto the sail cover, I had sewed into the canvas cover on my bass boat.. Puts out 1.5 -3 amps. Newer ones are capable of higher, but I have found this is adequate to keep three deep cycles charged. With an rv you can use a solid one, and just lay it on the dash, they make them that plug in to the cigarette lighter. Silicon Solar is one outfit

Whitelightning

You way will not get 1.5 to 3 amps at 14 volts out of a 6 x 18 inch cell. No way, put a amp meter and you will find maybe 600 to 900 milliamps or a bit more. It will take a lot bigger cell to make 3 amps. Also there is no problem about charging them in parallel as long as they are both newer style battieries. Back when maintainance free first came out and the older style lead acids where still around, you did not want to hook them together all the time or charge them together either as the newer battieries have a bit higher charging voltage and cutoff.

----------------- The SnoMan

I agree with you ... he would need a 50 watt solar panel (min) to get that kind of current and only on bright, sunny days. A 50 watt panel is going to be about 1 foot wide by almost 3 feet long.

He may want to consider adding a battery isolator. There are devices that sense the difference in the voltage of two batteries and automatically connect the lower of the two to the charger. I had an RV based on a E-450 chassis that was set up like this. While driving, the alternator charged both the engine battery and the two, 6 volt in series RV "house" battery as determined by the isolator. When parked and hooked up to shore power, the built-in RV charger would charge to house battery, isolating the engine battery unless it's voltage dropped for some reason.

Eisboch

This is a good sound suggestion :)

----------------- The SnoMan

The coach battery ought to be isolated from the chassis battery.

Battery isolators are generally just two diodes set into a heat sink. The diodes direct current from the charger or alternator into each of the batteries but prevents reverse flow when one battery is at a lower voltage. That means you can run the house battery in an RV flat and the start battery will not be discharged.

There is the small matter of the forward bias voltage across the diode, .5 volts or so but charge source voltages are usually high enough to still charge the batteries fully. They are a very simple three terminal device and can be installed by the average handyman.

Stephen N.