Electrical problem: batteries are draining when truck is parked for three weeks or longer (less days by colder weather) camper unplugged. Batteries replaced. I've also got an Isolater installed.

Ask them for a parasitic draw test, measure the amps as they leave the battery. use the amount as a clue. Operate everything looking for obvious problems. first. Delete circuits one by one during the draw test. Watch the meter for the big change. Disconnect components one by one. Add-ons can be suspects because of the installation methods sometimes uses and misused because of limited access and unfamiliarity with the electrical systems which constantly are changed or redesigned. After trying the things you can think of, get the power distribution and fuse panel info. Delete the circuits you are more unfamiliar with. Since it is a 3 day er, I would do the math. Lets say you have the known hours, and a 40 amp hour battery. How many amps can accomplish a no start?.............. Your technician is supposed to know............... What if it was a bulb with a crossed filament ? What's that ? it works when its not supposed to, or, merely has gone dark but the filament is sending the power to ground at a rate of a quarter amp. savvy? Any low amp circuit(s) could do it. It would not blow a fuse at that low amount. What systems or lights have a malfunction? Start there. You could inspect them all yourself. If you need help and a draw test, your RV technician at an RV dealer is like superman in coveralls. Bring your muffins and Thermos to share. perhaps.

Thank you! (Will try it again), even though I previously did this with the dealer and they said they found less than a .5 (something really low that I don't remember) that wouldn't be the cause as he felt it was energy used to operate all the miscellaneous operations in truck. But - I need to start somewhere- although they should have a record on file. Thanks for your response!

(.5 volts ?) (.5 mV ?) (.5 Amps?) (.5 mA) (.5 ohms?) try and find out what the readings are. The vehicle must be acting up while the reading is read, or you have to wigglle test and operate, or attempt items that can cause it. like if it has a good few days, starting charging then holding. Then you carry a passenger. then it acts up lets just say, you would operate that side, suspect those components. inspect light bulbs any time for darkened glass, disconnect add ons to eliminate them

ask how many is the reading, then you can duplicate it at home and watch for a change in the reading if you check it every few days trying to catch it, like after a notable drop in starting battery voltage. You can get a couple cheap DVOM meters and take readings at home on your available attention to it. I had a girl lose her whole car once after buying a bunch of recommended guesses. All she needed was a few readings and being patient. Next time I asked she had spent large amounts and then gave up. I never recommend that. Having a meter to switch-on that reads battery volts is safe, easy, temporary, and tells you if it was draining while it sat.

Thank you Dannyl - I will try that!

If you can measure volts remaining, you verify battery discharge. If you measure amps as they leave,by one cable, you measure amp draw. If battery discharges but no amp draw was read? that's the battery. The KAM power, (keep alive memory) is the truck's engine computer normal draw. other normal draw can add making the reading greater. we need your reading and to find what your "normals" add up to. Add on parts , non GM are very suspect. since they were added by non engineering personel. They can be entertainment, towing, camping, devices related, charger related. the parasites that the maker did not have and could be dealer installed or whomever. not blaming, just measuring because of dry camp need as it could be acceptable? we will see.

Thanks for your help- I will do the things you suggest