T6 Camper van battery drain, tips appreciated

Had the battery replaced on my T6 just before end of warranty so about 15 months ago. Problem is it keeps going flat after about 2-3 days of not being used. I have a leisure battery system that I fitted myself using a Ctek 250SE. At first I though this may be the issue so I removed the fuse and fully charged the battery. 2 days later totally flat again (actually it did just about fire) but voltage from the battery pre startup low at <12v.

On tickover the voltage to the battery seems healthily 14v+

There must be some other drain, any tips on where to begin????

Aftermarket head unit?

My 2010 t5.1 has been awful din e I changed jobs ,so get to leave it stood all week. Pretty certain all that is draining it , is alarm / immobiliser. Four days max, usually 3 between parking up after a 200 mile weekend and me getting the charger out. Again.

Aftermarket head unit?

No all standard. Outside of the Leisure system installed everything is standard. The leisure system has a lot such as LED lights, Fridge, Diesel heater, water pump, adjustable LED lights and USB etc but this has been isolated and all of those items are switched through a separate panel (the diesel heater controller uses power when off)

Absolutely certain you have nothing plugged in that is using power and draining battery? I had an iPod plugged into the dedicated USB plug in the car and if I didn’t drive car for 2 days when I started it the battery would show as being low…a decent drive fixed that, but after unplugging iPod from car the battery issue stopped.

I miss the music but prefer not worrying about flattening the battery. I then forget to take iPod out to car hence no music of choice.

Is the warranty battery another Moll battery? If so, I’d put money on it being that.
Also check that there are no extra connections on your battery earth. These all need to go on a chassis earth or your battery monitoring won’t work correctly.

Is the warranty battery another Moll battery? If so, I’d put money on it being that.

I’d forgotten but VW did have an issue with batteries around 2017. Our Polo got a new one under warranty.

I would have thought the replacement would be OK though but you never know.

I’ve got a 2019 T6 that had a duff Moll, they’ve replaced it with another duffer and won’t entertain another swap at the minute. Going to fit and code a decent battery in myself if I can’t get them to swap it before my warranty runs out

Had a camper conversion that had the original interior lights left connected-one on the step (fairly normal) but the other was the original roof light that was now tucked away on the inside of the roof cupboard by the tailgate. It was so easy to turn the bloody thing on without realising…well, until the battery lost its charge!

It’s multimeter time. What’s the resting voltage on this new battery? If it’s OK, switch to measuring amps and pulling fuses one at a time to narrow down the problem (google find battery drain in car).
Don’t get me wrong – asking people for possibilities is a legitimate prior move (I’d do it!). But I think that’s the point you are at.

Is the warranty battery another Moll battery?

No its a Vantra.

Absolutely certain you have nothing plugged in that is using power and draining battery?

Yes double checked.

Nothing else attached directly to the battery (that shouldnt be there)

But I think that’s the point you are at.

Yep, I need to put a clamp on it and start tracing fuses….

Agreed on the multimeter to diagnose.

It’s not got a dashcam has it? Or a reverse camera that’s always powered on (the camera, not the display)

It’s not got a dashcam has it?

Yes but disconnected that a while ago as that was permanently on

When the battery was replaced, did somebody plug a computer in and tell the van it had had a new battery fitted?

If it’s not, then you’ll get those exact symptoms. The BMS needs to know there is a new battery, otherwise it doesn’t put enough charge back into the battery.

Update: Disconnected negative terminal and using my multimeter found the draw was almost 2 amps when ignition off…..

“infotainment system” was drawing about 1.1-2 amps, after removal down to about .72 which is still very high. Removed a number of fuses with no success so still not resolved the issue fully but had a dose of Flu this week and the crouching down etc was making me nauseous so it will have to wait for a few days…

Did you let the van sit for at least 30minutes, and then add in an ammeter without breaking the circuit, or activating any door switches?

Most modern vehicles take 5-20minutes to fully shutdown, and if you disconnect/reconnect the battery, some modules will wake up again. The same for pulling fuses.

A battery drain test isn’t a simple test to conduct on modern vehicles.

Did you let the van sit for at least 30minutes, and then add in an ammeter without breaking the circuit, or activating any door switches?

Taped up the door switch as the fusebox is in the drivers footwell but didnt wait 30, thanks for the tip. need to revisit methodically on Tuesday I think.

To rule out my battery being at fault I removed it from the van and left it on my smart charger (CTEK MXS5) for around 10 hours.
After settling it showed 12.79v. 12 hours later it is reading 12:42v. I will keep testing it for another couple of days but does this seem normal to see this small drop with nothing connected at all?

After settling it showed 12.79v

How long after you disconnected the charger was this?

Which leads me to

12 hours later it is reading 12:42v

If the voltage measurements are accurate that’s not a good sign for your battery. After charging, your voltage should be in excess of 13V due to the surface charge on the plates. This can remain for up to 24 hours after charging is complete. Once the surface charge has dissipated a 12V battery in a fully charged state should be producing between 12.6 & 12.7V If the battery has for whatever reason been deeply discharged it can be permanently damaged.

It might be worth having the battery tested at somewhere like your local tyre/exhaust/battery depot. It takes about 30 seconds & every time I’ve had to do this it’s been free. The test will give the cold cranking amps CCA’s & the battery’s reserve capacity.

Can’t shed any light on the current draw but it’s definitely not right. 14V plus whilst the engine is running sounds like the alternator is working properly. Have you got a solar panel fitted? If not wired correctly through a blocking diode you battery can discharge through the panel.

Good luck.

Thanks for the reply @Davesport

It was about 20 mins after disconnection.

No I dont have any Solar. The CTEK 250 unit does have a built in controller but havent added any yet.

I will find somewhere to have it tested. Thanks again.

Thanks for the reply @Davesport

It was about 20 mins after disconnection.

No I dont have any Solar. The CTEK 250 unit does have a built in controller but havent added any yet.

I will find somewhere to have it tested. Thanks again.

Just thinking out loud & you’ve probably thought of this already. If your present battery is gubbed don’t fit the new one until you find out what’s drawing the mystery current. Deep discharge for lead acid batteries equals early death.

Sounds like you are doing things correctly but just incase. I found this video was very good in making sure you are correctly checking the parasitic drain on your car. Covers things like making sure door latches are shut etc … and covers a way to check the current drain without discounting the battery or pulling fuses out so makes it a little quicker to check.

When checking battery voltage you should wait a couple hours at least after charging to wait for the surface change to disappear otherwise you get a false reading with higher figures.

But it sounds like the battery is faulty I would not expect a good battery to drop to 12.4v after 12 hours.

Pulling fuses out to check drain is not that reliable, because when you pull one out and put it back in that module might start back up and start consuming current. I tried this and it was utterly inconclusive.

In my case the drain was because I’d replaced some failed control modules with later software versions, and these needed an upgraded CANBUS gateway to prevent battery drain. I knew this was an issue for upgrading the radio but it didn’t occur to me it would apply to other modules too.

Thanks everyone. The plot thickens… Put the original battery back on as planned to go and collect a new one. Started fine and drove for about 15 mins. At lights I noticed the leisure readout display was at around 12.xx which would normally be around 14.xx as it would be usually be picking up power via the split charge. This indicated something was wrong so I came home and with the engine running tested the van battery (expecting it to be circa 14.xx) and that was actually <12.xx which may indicate an alternator issue……. As expected turned off and wouldnt restart.

Plot twist: another check of the battery reading 12.30 which would indicate it has discharged and is recovering??? points more to the alternator….

Thanks everyone. The plot thickens… Put the original battery back on as planned to go and collect a new one. Started fine and drove for about 15 mins. At lights I noticed the leisure readout display was at around 12.xx which would normally be around 14.xx as it would be usually be picking up power via the split charge. This indicated something was wrong so I came home and with the engine running tested the van battery (expecting it to be circa 14.xx) and that was actually <12.xx which may indicate an alternator issue……. As expected turned off and wouldnt restart.

Plot twist: another check of the battery reading 12.30 which would indicate it has discharged and is recovering??? points more to the alternator….

Hmm. I wonder if it’s worth checking the earth from the battery to the chassis? If you can get your voltmeter probes onto either end of the earth lead. Set scale to DC volts & get someone to crank the engine while you watch the display. Anything above 1V over the length of the earth lead would indicate higher than desired resistance. Might be a simple first step. It’s irrelevant that the engine isn’t going to start. Visually check both ends of the lead/clamps/crimps.

If that proves ok you need to charge the battery up & test the alternator output again with the engine running. Voltages as previously discussed. 14 to 14.4 at tickover; should increase slightly when revved a bit. Anything below 13.5 & the battery won’t be charging.

D.

I’m going to re-quote this post, which was never answered.

When the battery was replaced, did somebody plug a computer in and tell the van it had had a new battery fitted?

If it’s not, then you’ll get those exact symptoms. The BMS needs to know there is a new battery, otherwise it doesn’t put enough charge back into the battery.

The Battery Monitoring System on newer VW’s is pretty rubbish, as it won’t correct for if a new battery is fitted, unless you tell it.
It allows for battery degradation, so if you fit a new battery, it will only put the same level of charge back in, as if it was still a failing battery, which leads to undercharging.
You need to tell the BMS that there is anew battery, so it can learn the new battery.

Measuring the charging voltage on anything with a smart charging system is pretty meaningless, as the alternator voltage changes depending on various factors. It can go from 12.5V to 15V, and the only real way to test the alternator is working correctly, is using diagnostic kit to trigger an alternator test.

My T5 started losing charge – flat after a few days unused. I thought i had a drain from somewhere, but it was soon obvious that the battery was at fault. Eurocar parts gave me a refund – Bosch battery, 2 years old with 5 yer warranty. New Yuasa battery fitted and no drain symptoms at all.

I miss the music but prefer not worrying about flattening the battery. I then forget to take iPod out to car hence no music of choice.

So why don’t you just unplug the iPod and leave it in the car? Just pull the lead out from where it’s plugged, then plug it back in when you need it. I frankly don’t see what the issue is here.

Something else has just occurred to me – are the keys kept anywhere near where the van’s parked! I had a training session today on charging and jump-starting hybrid and EV’s, and ideally the keys should be kept at least five meters away when the vehicle is left, because it can still detect the key, and it stops the car shutting down completely and going to ‘sleep’. This was completely new information to me.

The Battery Monitoring System on newer VW’s is pretty rubbish, as it won’t correct for if a new battery is fitted, unless you tell it.
It allows for battery degradation, so if you fit a new battery, it will only put the same level of charge back in, as if it was still a failing battery, which leads to undercharging.
You need to tell the BMS that there is anew battery, so it can learn the new battery.

Measuring the charging voltage on anything with a smart charging system is pretty meaningless, as the alternator voltage changes depending on various factors. It can go from 12.5V to 15V, and the only real way to test the alternator is working correctly, is using diagnostic kit to trigger an alternator test.

I’m all ears as I also own a T6. This is news to me & something I’ll remember for future reference. I hope I’m not the cause of you repeating yourself :o)

I’m going to re-quote this post, which was never answered.

Thanks for this I did take note. I have bought a new battery and fitted it and scouring other forums this came up. Also was mentioned by Halfords as part of their fitting service. I do have it booked in with a mechanic mate on Friday so hopefully he can look at this to save me damaging the new one.

Another interesting fact I wasnt aware of is that the alternator only charges up to around 80% and then stops, by design. To do with the start stop system apparently. This may explain my concern that the alternator was not charging when I fitted the old (fully charged battery yesterday) Possibly the alternator was waiting for its charge to drop to 80% before providing charge. Interestingly this does impact the leisure battery as it cant harness any spare charge as none is being generated…
Anyway off for a nights stealth camp so hopefully the alternator will kick in after the battery has been used for an hour so’s drive.

To explain the issue a bit better, say your old battery has dropped to only 10Ah capacity. You fit a new battery, but the BMS still thinks the battery only has 10Ah, despite your new battery being near 100Ah.
As the BMS still thinks your battery only has 10Ah worth of capacity, it only puts ever puts 10Ah worth of charge back in. However batteries are never 100% efficient, so over a period of days/weeks (usually takes a couple weeks from experience), your 100Ah battery eventually drops to only having 10Ah worth of charge, just like your old battery.

Your auxiliary battery is a bit different, as it should be connected on the vehicle side the main battery current sensor, so as long your split charge system knows the vehicle is running (you really want to be running a DCDC convertor on anything Euro 6 to ensure the aux battery gets charged consistently), it should still get charged without being affected by how the main battery charging is being regulated.

Modern BMS’s will typically set alternator voltage to around 12.5V after starting, so the battery gets charged slightly and avoid putting too strain on things. It will then usually rise a few minutes later if the vehicle is not driven, but if the vehicle is driven, regenerative braking will be used to boost alternator voltage as high as the battery fitted can handle on overrun, to maximise energy recovery.
However, whereas other manufacturer’s will keep the voltage high regardless of battery capacity, and let the battery absorb as much charge as it wants, VW only put in as much charge as they calculate the battery should need.