Some cars have a relay socket, so you can install a charging relay for
charging batteries in travel trailers only while the vehicle is running.
Otherwise, get a battery combiner from West Marine etc. for about $80 and
connect one end to the car circuit and the other to the trolling battery.
Bill

"Rod McInnis" wrote in message
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wrote in message
om...


I'd also like to charge that trolling battery as I drive around. I
know most will tell me to get a fancy isolator and connect it to all
sorts of places in the truck.

What sort of trailer light connector do you currently have?

If you have the 7 conductor round RV style connector then there is a good
chance that you are already wired for supplying 12 volts to the trailer.
If
it is properly wired, the 12 volt connection should have a fuse/circuit
breaker on the vehicle.

You can simply make a new adapter that provides a 4 pin pigtail for the
trailer lights and brings out the 12v and ground to connect to the boat
battery.

You can do a lot more work to assure that you had isolation, but it
probably
isn't worthwhile. Note that any diode isolation you install is going to
dramatically reduce the charging current to the boat battery.

Rod McInnis