Dead batteries

[mmorris]

On Wednesday, we brought home our new, to us, Cruiser and left it plugged in to the tow vehicle. We blew a tire on the 1.5 hour trip home, so this morning I had an appointment to get new tires. I got in the truck and both batteries were dead. Since 2004, this truck has only not started one other time. The batteries were never drained when I left the previous RV plugged in to the tow vehicle.

I checked inside to see if the furnace, TV booster, or anything else was on and found nothing. I'm thinking the only thing it might be is that an electric brake was stuck on. I haven't checked this yet since I'm charging up both batteries in the Dodge diesel.

Anyone else had this problem? Could it be the converter/inverter? What else should I check?

Thanks in advance.

Monte

[woodwalker]

Could be that if the batteries are 04 they are shot

[mmorris]

LOL.

[Dayle1]

It is unlikely you have an inverter in that unit unless added by the previous owner. The converter uses 110V AC and produces 12V DC and unless you had shore power connected, it was doing nothing, even then it would charge the batteries, not discharge them. More likely, the trailer battery has a bad cell, low on water or something and it drained the truck batteries. If the electric brakes were on via the breakaway cable, you wouldn't have been able to tow the trailer.

One other possibility is the refer, depending on model, some have a switch hidden inside the door frame at the top. It controls a 12V DC heating element in the door gasket to reduce moisture condensation, and it works even if the refer is turned off. So it can drain the RV battery and then the truck battery if it is on.

Anyway, it is never a good idea to leave the umbilical cord hooked between truck and trailer for very long w/o the engine running or shore power connected.

[mmorris]

I once had a trailer brake "stick" that continued to draw current. I found out when I was underneath it and heard a small humming sound. I used a compass next to the wheel and it deflected; showing current. None of the others were humming. I went to the truck and stepped on the brake a few times and the humming stopped. I'm not sure what it was, but I did rewire all the brakes in the 5er and it never happened again.

I charged up both truck batteries (and the RV) today and they are reading only 12.9 volts (the RV one is fine). I checked when I last replaced them and it was in 2010. I ordered new ones today.

Thanks for the advice!

[Papa-T]

Originally Posted by woodwalker

Could be that if the batteries are 04 they are shot

Agree 12 years on a set of batteries is a long stretch. Let us know what you find out.

[Dayle1]

Originally Posted by mmorris

I once had a trailer brake "stick" that continued to draw current. I found out when I was underneath it and heard a small humming sound. I used a compass next to the wheel and it deflected; showing current. None of the others were humming. I went to the truck and stepped on the brake a few times and the humming stopped. I'm not sure what it was, but I did rewire all the brakes in the 5er and it never happened again.

I charged up both truck batteries (and the RV) today and they are reading only 12.9 volts (the RV one is fine). I checked when I last replaced them and it was in 2010. I ordered new ones today.

Thanks for the advice!

Trailer brakes will only hum if power is coming from the brake controller in the truck. Brake controllers work by 'chopping' the DC power, switching it on and off many times per second. This is how the magnet strength is varied and causes the hum. If power is via the break away switch, there will be no hum as full DC current is flowing all the time for max magnet strength. But a compass will react to the magnet regardless of the power source.