battery, charger or wiring issue?

I was able to measure the current on the red incoming wiring from the battery and with all DC loads turned off, there is 0.2 amps. That seems to preclude the idea of a mystery load.

The battery drains to nothing in just a few days when just sitting by itself with all 12 volt loads turned off (that can be turned off). I have also wondered about a mystery load draining the battery. The only remaining continuous DC loads should be the usual radio, propane detector, etc. No tank heaters or anything else like that.

I have a fancy $10 Harbor Freight multimeter that I just noticed will read up to 10 amps DC. Will see what I can read on each 12V circuit at the panel.

BFL13 wrote:
You have 12.4 at disconnected battery but when connected, no shore power, you get 11.1. So your rig has something "on" that is bringing the battery down to 11.1 as its "loaded voltage" from that mystery load.

There is no voltage drop unless there are amps on that wire, so that proves there is something "on"

When you plug in, the converter is able to handle whatever that load is and stay at 13.7

So what is the mystery load? One suspect is always the breakaway switch that leaves the trailer brakes drawing 12 amps when the pin is pulled on that. However that should also mean you can't move the trailer, so if this battery problem was going on when camping and you drove home then it should have been a tough pull!

Another is if you have heated water tanks and that is "on"

Maybe a short somewhere, likely on the tongue which is exposed to rain etc.

You could pull each fuse on your DC fuse panel, one at a time until the battery voltage jumps back to 12.x, which would identify the guilty circuit. Then you have to chase down what on that circuit is causing the draw. Say a wet lamp in the shower. But not everything that uses the battery is fused at that panel.

You have 12.4 at disconnected battery but when connected, no shore power, you get 11.1. So your rig has something "on" that is bringing the battery down to 11.1 as its "loaded voltage" from that mystery load.

There is no voltage drop unless there are amps on that wire, so that proves there is something "on"

When you plug in, the converter is able to handle whatever that load is and stay at 13.7

So what is the mystery load? One suspect is always the breakaway switch that leaves the trailer brakes drawing 12 amps when the pin is pulled on that. However that should also mean you can't move the trailer, so if this battery problem was going on when camping and you drove home then it should have been a tough pull!

Another is if you have heated water tanks and that is "on"

Maybe a short somewhere, likely on the tongue which is exposed to rain etc.

You could pull each fuse on your DC fuse panel, one at a time until the battery voltage jumps back to 12.x, which would identify the guilty circuit. Then you have to chase down what on that circuit is causing the draw. Say a wet lamp in the shower. But not everything that uses the battery is fused at that panel.

Responses in red. What I don't understand is why the voltage reads 11.1 volts at the battery with shore power off, cables connected to battery and all 12VDC loads turned off. Shorted cell and not capable of delivering under even a minimal load?

With shore power turned off and battery cables connected, voltage at the converter is 10.8V (while 11.1V at battery). Is 0.3 volts drop okay with all DC loads turned off?

With a bunch of lights (LED) turned on, battery connected and shore power off, the voltage at the battery drops to 9.8 volts.

The thunk I mentioned above when plugging fuses back in turns out to be the 2 Maxxair fans we have.

RoyB wrote:
Fix one thing at atime... FIRST BIG CHECk is to measure the BATTERY at the termnals with SHORE POWER TURNED OFF.. If the battery is fully charged it should read 12.6-7VDC. With shore power off and battery cables connected, voltage at the battery reads 11.1 volts. If battery pos. cable is disconnected, the battery by itself reads 12.4 volts.


Leaving the meter connected to the battery terminals then turn on SHORE POWER CABLE. The DC VOLATGE at the battery terminal should jump up to 13.6VDC Voltage at the battery reads 13.7 with shore power turned back on.

If it does not this means there is a disconnect somewhere between the CONVERTER DC OUTPUT termials and the BATTERY TERMINALs.

Get that resolved first then we can go from there...

Most likely a blown fuse between the Battery Terminals and the CONVERTER/CHARGER. Might also be your two REVERSE POLARITY fuses blown. Reverse polarity fuses are good - checked with ohmeter. As mentioned previously, connections at the mini circuit breaker in the A-frame look quite corroded. Tried to clean as best I could but have no sandpaper or emery cloth and can't get one nut off the stud. Re-connected all wires to the same terminal and no improvement.


If it blows the same fuses again then most likely the BATTERY has shorted cells. I've had that thought in the back of my mind as a possibility but wouldn't have suspected it on a year old battery (interstate)? Had that happen once on a battery in our skidsteer loader and didn't figure it out until taking it to a battery shop for a test.

This occurs when being left on the 13.6VDC Charge from the CONVERTER/CHARGER being ON for long periods of time and not monitoring the battery fluids. Once the fluids has been boiled out of the battery it will most of the time short out.

let us know what happens after doing these steps...

Fix one thing at atime... FIRST BIG CHECk is to measure the BATTERY at the termnals with SHORE POWER TURNED OFF.. If the battery is fully charged it should read 12.6-7VDC.

Leaving the meter connected to the battery terminals then turn on SHORE POWER CABLE. The DC VOLATGE at the battery terminal should jump up to 13.6VDC

If it does not this means there is a disconnect somewhere between the CONVERTER DC OUTPUT termials and the BATTERY TERMINALs.

Get that resolved first then we can go from there...

Most likely a blown fuse between the Battery Terminals and the CONVERTER/CHARGER. Might also be your two REVERSE POLARITY fuses blown.

If it blows the same fuses again then most likely the BATTERY has shorted cells.

This occurs when being left on the 13.6VDC Charge from the CONVERTER/CHARGER being ON for long periods of time and not monitoring the battery fluids. Once the fluids has been boiled out of the battery it will most of the time short out.

let us know what happens after doing these steps...

You still didn't say what the voltage is at the wires that go on the battery with shore power plugged in. The converter's 13.7 volts should show there.

You do get battery voltage to the DC panel so the path is not "open" so you should get the converter's 13.7 at the battery end on that same path.

If you are getting the 13.7 at the battery ok, there is nothing wrong with the converter/charger. What you have reported would then just mean the battery is no good anymore.

The battery isn't quite a year old yet, but the dealer didn't mark the battery date on it so I don't know how old it really is. If it does happen to be the battery, I hope it would be covered under warranty. The battery only gets use during the 30 minutes or less when breaking camp or setting up and has been kept charged by the converter charger all winter. It is the lo cost charger tho. and perhaps that is suspect?

2oldman wrote:
Voltage is not a particularly reliable measure of the health of a battery. Allowing a battery to go dead is not good for it at all. It's probably shot, but, you can easily verify with a good VOM when things start to dim.

Shore power off, with battery cables connected and no 12VDC loads, voltage at battery is 11.1. Why would open circuit battery voltage go from 12.4 to 11.1 with DC loads turned off?

Same as above, but with a bunch of lights on, voltage at battery drops to 9.8.

I noticed when I had all fuses pulled out a few days ago and was putting back in, the one labelled bedroom made a thunk sound like sort of like there was a solenoid being energized. Not sure if normal and related to the voltage issue.

The connections at the mini circuit breaker are quite corroded and I couldn't get one nut to budge. I have no sandpaper with me and I cleaned what I could with a screwdriver and re-attached all 3 wires to one stud to test - no change but could still be a bad connection. Frame ground *looks* okay but can't get the lug off without a nutdriver.

BFL13 wrote:
Need more info.

With trailer plugged in check the voltage at the wires that go on the battery. should be that same 13.7 volts as at the panel.

With trailer not plugged in and battery showing 12.4 with no load, now turn on some lights. What happens to the battery voltage?

Don't forget to ask, "80% of what?"

How is the water level in the battery? Probably boiling out nicely due to shorted cell.

Voltage is not a particularly reliable measure of the health of a battery. Allowing a battery to go dead is not good for it at all. It's probably shot, but, you can easily verify with a good VOM when things start to dim.