Batteries discharging while driving

PAylor · January 31, 2023

We have a fifth wheel with batteries less than a year old. We also have a residential refrigerator. Recently the batteries have started discharging while we driving. The inverter is on and the 7 pin cord is plugged into the truck. When we turn off the inverter the battery level remain normal. But then the refrigerator is off.

Any ideas on how to find out what's wrong?

Thanks in advance!

Edited January 31, 2023 by Kirk W
Remove excess empty space

Darryl&Rita · January 31, 2023

You're using more battery than is being replaced. The RV charge wiring on most vehicles is barely adequate with no load on the RV batteries. The system likely never worked ideally, and new batteries only masked the issue. There's a number of write-ups online, regarding upgrading charge line size, connections, and voltage output. Time to do some research in that direction.

rpsinc · January 31, 2023

Have you confirmed that the alternator is in fact providing 12V at the 7 pin plug?

And is the wire size sufficient to capitalize on the amp output of the alternator?

Have you considered a solar panel/s that would provide charging irregardless of the engine running?

Perhaps increasing the battery bank could also be considered. That could allow for capacity to run your refer until you are able to get to destination OR until you stopped for some time to run a smallish generator.

Kirk W · January 31, 2023

I would agree with what Darryl has already posted. It is possible that for some reason your trailer isn't getting the 12V normally supplied to check that first as it likely is fused on your tow truck. I would get out the meter first and check the plug for the umbilical cord.

If pin 4 has 12V available you can then go measure across the trailer battery first without the truck connected, then with it connected and running check again for a voltage increase. If it is there, the next thing to consider is wire size as small wires do limit the amount of current available.

RV_ · January 31, 2023

How old is the fridge? Below I linked to an article about them using more power for a number of reasons. As well, if you only experience it on the road only recently have you started filling it up before getting on the road?

If you are getting power at the 12 volt pigtail then it is the inverter/wiring inside the RV, or the reefer itself. Or, since the batteries are new they could be defective or have bad cells.

https://homeguides.sfgate.com/grow-herb-garden-indoor-outdoor-13771633.html

Edited January 31, 2023 by RV_