Suggestions for Flat Battery Investigation

[dbrock]

Merry Christmas everyone!

I hope you are all enjoying your turkey dinners, but if you should have a few idle moments this festive season I would be grateful for suggestions on how I might diagnose a flat battery problem.

The van is a 2016 T6 converted in 2023 with a leisure battery professionally installed under the drivers seat. Charging is via a Sargent EC155 with an EC50 control panel. The van developed a reversing senor fault. On further investigation, the electrics to the 13 pin towing plug also did not work. It went to a garage 4 weeks ago who found that the reversing sensors and the control module worked fine, but that there is a wiring fault somewhere between where the wires enter the bodywork at the rear nearside and the control module at the front. That will require a strip down of the interior which is booked for January.

Yesterday, I checked on the van and found both batteries to be completely flat. The batteries have never run flat before, even if left for a couple of months. I am usually meticulous in turning everything off, but there is a very small possibility that I may have inadvertently left something on. I thought that there was separation between the leisure battery and the vehicle battery, so I am surprised that they are both flat.

Does anyone have any suggestions for how both batteries ran flat in just 4 weeks and what investigations might shed some light on the remedy?

 

[whodat]

What do you mean by flat? 0v or 10v?
For the wiring fault, it might be easier just to run another cable if it means not stripping anything out - but I don't know about running cables in this van so maybe not!

 

[dbrock]

By flat, I mean the vehicle battery was around 11.4v with enough power to operate the central locking but not enough amps to turn over the starter motor. I am not sure how to measure the leisure battery as it is buried away under the drivers seat. With the vehicle battery removed I still had 2.5V across the terminals. This could be the leisure battery voltage or some other residual charge.

 

[sams-vans]

If you have a multimeter, look up parasitic draw. Although your situation might be more than parasitic. It’s a process of finding which circuit is drawing current. Then finding the device, light, thingy etc that’s on/failing enough to draw current. That’s about the best I can do from 10,000 feet.

 

[roadtripper]

It takes a remarkably small current to empty a battery quickly if it's there 24/7 - even a USB converter can do it in about 3 weeks.

If you have factory 13 pin electrics then how did you check it wasn't working? The factory control module needs 2 out of the four indicator and side light circuits to have an actual bulb in to trigger the trailer detection. It's known not to be reliable on LED and if you just tested with a multimeter it may have seemed dead.

Your best course of action right now is to trace the wiring in the van - you should have a wiring diagram from the converters but often these are either missing or too simplistic. Without that there are too many variables to really be able to help, whereas folks can help if you have one - or at least start tracing so that we can help you build a wiring diagram.

 

[dbrock]

Thanks for your helpful tips. I tested the 13 pin plug by inserting a known working tow board and starting the engine. Nothing happened. I have ordered a clamp multimeter meter and will start hunting for the parasitic draw.

 

[Deaky]

Check there are no additional connections to the starter battery -ve post