Dual batteries

[smjrhp1]

Hi;
New to Forum.
I purchased a 2001 E350 XL van with 7.3 diesel. This van was used for Handicap service in Texas then ended up at a dealer in CA, where I bought it.
The van has performed well since purchase (12-20), I purchased shop repair manuals and notice that a switch was installed to run the back heater. Don't know why, since there was a switch already on the dash. Anyway, I just found it and used it to run the back fan for heating the van and shut it down yesterday and today I found the batteries (dual) dead. So, I'll have to verify this, but I suspect they used an live wire that doesn't shut off when the ignition is turned off, which has drained both batteries.
I checked the manuals and didn't see any warnings about charging the batteries in while in the vehicle.
But I tossing this here to see if any of you know that it wouldn't be a good ideal, to charge up the system while in the vehicle.
Thanks for the time and info.
Great sight.
Jim

[2000goshen]

yeah charge away set to 12 volt and hook it up to the battery in the engine compartment like normal.
If your needing justification then you can look at it just like your battery charger is a smaller and weaker alternator which charges the battery in your vehicle all the time! Good luck with the van.

As for the rear heat switch and circuit you will just have to verify what's wrong. maybe it was just a coincidence? then again maybe not, if the fan is working normally with the switch it should be fine. the switch shuts off with the ignition.

[smjrhp1]

2000goshen;
Thanks for the reply, I was just concerned about the electronic gismos.
Jim

[smjrhp1]

Just to update.
It was the rear fan. It seems someone thought it needed to be powered off of one of the power plugin (cig lighter). So, it continued to run after the key was turned off.
Now, it running like it was, no battery drain.
I'm going to reconnect the proper switch and install the power adapter that should be there.
Jim