My camper battery is not charging, and I'm struggling to determine why not...

After a weekend away, my camper battery voltage is 11.65 volts.

If I unplug the trailer cable at the camper, and check across the "-" and "+" (charge) contacts of the 7-pole plug on the end of the cable, I get a reading of 13.8 v at idle.

If I check each of the matching poles of the plug socket, I can verify a circuit to the "-" and "+" leads at the camper battery. However if I plug the cable end into the socket, I still have 11.65 v at the battery. :-(. In fact its 11.65 at the fuse connector just upstream of the plug.

I'm sure there is a quite simple explanation for this, but for the life of me I don't see it right now.

 

Has it worked before? (apparently, yes, I suppose)

I would probably look for a ground problem first, either the battery to camper or camper to truck could be in a bad shape (e.g. loose/corroded).

Could be corrosion in the plug or any other connector, could be a damaged wire, or a loose connector.

Depending on the gauge of the wires and the overall situation, what you see could also be normal. The line from the alternator to the camper battery is pretty long. Depending on wire gauge, length and current, you can expect a significant voltage drop. When you measure the open connector, there is no current flowing to the camper and you measure the "idle" voltage of the line. Once connected, if your (empty) battery charges at 10 amps or whatever, the voltage drop can be significant.
Here is a link to an online calculator that lets you calculate the expected voltage drop: https://www.calculator.net/voltage-drop-calculator.html

Could also be a dead battery. What happens when you charge the battery from an external 120V connection? Does that work?

 

What Burro said. Bad connection is the most probable so look closely for that first. Even with a bad battery, your meter should show a positive change in voltage when you connections are good.

 

Many thanks for the responses!

Well, when I went out yesterday to do some more noodling on this, I discovered that the battery voltage was down to 9.6v (from 11.65v the previous evening). Topped up the water (it was low), and put it on "reconditioning" mode on my smart charger, and right now, almost 24 hours later, its still only on stage 4 (of 8). So its looking like maybe my battery is a goner... (Bummer, its only 3 years old, and I keep it regularly topped up).

Thanks again for the ideas & suggestions!

 

 

Disconnect the battery and measure the voltage on just the cables. with the camper on the shoreline or while on the seven pin.. You should see the converter voltage or nearly so on the cables. That will tell you if you have a viable connection. Do not spend the money on a battery until you resolve this issue. Have you measured the voltage at the junction box on the trailer while connected to the seven pin?

 

Okay, so I let the battery charger finish the "reconditioning" cycle, and measured just over 13 volts an the battery. Let it sit overnight, and still 13 volts, so far so good.

This evening I backed the truck up to where the camper is parked, and ran the cable across from the trailer light socket. With no battery in the camper, I get just over 14 volts on the battery terminals in the camper, with the truck running. So the trailer connection is all good. (Even tried reversing the cable, in case it was cross-wired, but still good.)

So I put the battery back in the camper, and now see 13.8v with the truck running. So now its working, but I'm no closer to figuring out why it wasn't working before. The only thing I changed is adding water to the battery (it was really low) and running the battery through a recharge cycle on my genius charger.

This is not the first time this has mysteriously stopped and restarted working. I spent a couple of hours troubleshooting this a couple of years ago, in the Walmart parking lot in Duncan, BC, before just swapping the camper and truck batteries to get it charged, and finding when I swapped them back that the camper battery was now charging.??

I'm assuming that the cable and connections are OK, because I've checked and re-checked them. So the problem must be between the socket and the battery on the camper... i.e it presumably runs through the rectifier and fuse panel before it heads back to the battery. Is there an automated switch to toggle between shore, battery and truck power? (The only switch I see is a trip switch on the shore power feed.) Or should the 12V feed from the truck run directly to the battery, and all interior lights, pump, etc draw from that? As far as I know my rectifier doesn't charge the battery, its an older model (1996 Timberline) and the rectifier looks pretty ratty. Maybe time to replace with a more modern unit?

I made sure everything was switched off in the camper, so there should be nothing drawing power, and will check battery voltage again tomorrow to verify that its holding charge...

 

Very low water level can play a large role in whether a battery will charge and how long it lasts for sure, but just as you are now you should see a charge voltage which matches the charging source. When I am working on the lot, a great many campers that come in arrive with dead or no battery, but I can still run everything by just plugging in a shoreline. You should be able to do the same. Normally you will see 13.5 at the battery when plugged in as someone mentioned earlier.

So you have a 1996 camper with the original power converter? What manufacturer and model do you have in the camper?