Car battery power drain??

Sep 16, 2018
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Twice on over last weekend the battery on the car failed when connected to the caravan, the first at home about to set off, ba ked up then coupled up for 10 minutes and the battery was dead. Next time on the way home after 60 miles of driving stopped for break and the battery was dead again. Both times started with a jump, after the second time we didn't stop again until home, 140 miles later.

Either the battery is shot, or is there something in the van which could drain power that fast? Only thing running was the fridge and the ATC had a green light.

The van was serviced three weeks ago with no faults found.
 
Nov 11, 2009
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Twice on over last weekend the battery on the car failed when connected to the caravan, the first at home about to set off, ba ked up then coupled up for 10 minutes and the battery was dead. Next time on the way home after 60 miles of driving stopped for break and the battery was dead again. Both times started with a jump, after the second time we didn't stop again until home, 140 miles later.

Either the battery is shot, or is there something in the van which could drain power that fast? Only thing running was the fridge and the ATC had a green light.

The van was serviced three weeks ago with no faults found.
I would have the car battery checked as a first step. Then get the towbar electrics checked out. How old is it?
 
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Jun 16, 2020
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I would have your battery drop tested, Halfords, I find, will do this for free without pushing a new one onto you with a hard sell.

If the van was over draining, with a full or partial short. This should blow the fuse in the car. Often a 20 amp, in line fuse, and often placed close to the battery.

John
 
May 7, 2012
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It does sound like either the battery is dead or there is a problem with the towbar wiring. If the battery holds ts charge when the caravan is not being towed then it sounds like the wiring. I would follow Clive's advice.
 
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Thanks all, the batteries only 4 years old but will get it checked.
With regards to the van should anything draw power from the car when the ignition off (apart from lights, which were off)?


Meanwhile just very grateful for a couple in a transit van who powered our jump leads coming down from the Peak District.
 
Jun 16, 2020
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Thanks all, the batteries only 4 years old but will get it checked.
With regards to the van should anything draw power from the car when the ignition off (apart from lights, which were off)?


Meanwhile just very grateful for a couple in a transit van who powered our jump leads coming down from the Peak District.

There SHOULD not be any drain, except lights, as you say. But as R&A said in #5, if one of the relays, fridge or charging, is stuck in the on position that could be a problem,

Or, if there is a short between the permanent live and the fridge. That might be worth checking out.

John
 
May 10, 2020
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Ver (voltage sensing relay) duff? Should kick out when the car battery drops to 12.6 volts and back in when it sees 13.6 (I think). Canโ€™t remember off hand which pin on the tow bar socket supplies the fridge but a multimeter test on this pin should confirm correct switching.
cheers
R
 
Mar 29, 2021
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10 minutes connected wouldnt cause a car battery to drain, the amount of current that would pass would melt the cables rather than kill the battery.
Duff battery or car alternator
 
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Thanks all for your input, in the end we changed the car battery, then rather unexpectedly sold the van since our dream van came up for sale at a price we couldn't miss. Rather drastic but now solved :)
 
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Twice on over last weekend the battery on the car failed when connected to the caravan, the first at home about to set off, ba ked up then coupled up for 10 minutes and the battery was dead. Next time on the way home after 60 miles of driving stopped for break and the battery was dead again. Both times started with a jump, after the second time we didn't stop again until home, 140 miles later.

Either the battery is shot, or is there something in the van which could drain power that fast? Only thing running was the fridge and the ATC had a green light.

The van was serviced three weeks ago with no faults found.
Hi,
I take it battery does not discharge when caravan not connected.
Try a process of elimination,pull each dc fuse in turn and see when discharge stops.(battery stops flattening)
It's not something daft like keeping the road lights on even so battery should not go flat after such a short time.
Worth checking that car alternator is charging the car battery.
 
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Hi,
I take it battery does not discharge when caravan not connected.
Try a process of elimination,pull each dc fuse in turn and see when discharge stops.(battery stops flattening)
It's not something daft like keeping the road lights on even so battery should not go flat after such a short time.
Worth checking that car alternator is charging the car battery.
Thanks for the thought and taking the time to reply. However we sold and replaced the van, totally unplanned, a week ago.

What a crazy market !!!!
 
Oct 8, 2006
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I would have your battery drop tested, Halfords, I find, will do this for free without pushing a new one onto you with a hard sell.

If the van was over draining, with a full or partial short. This should blow the fuse in the car. Often a 20 amp, in line fuse, and often placed close to the battery.

John

Explain please: how can you have a 'partial' short circuit. In nearly 44 years in electronics I never came across such a situation.
 
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Thanks for the thought and taking the time to reply. However we sold and replaced the van, totally unplanned, a week ago.

What a crazy market !!!!
Hi,
Good hear you had a successful outcome,we don't usually get that.I just noticed the dates - I'll need to take heed from now on !
 
Sep 16, 2018
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I felt that as Darren.H said anything that would drain the battery in 10 minutes would do some serious wiring damage, or blow a fuse ( neither of which happened) therefore the most likely was a damaged battery, so was quite happy to change it.

Alternators fine, so with a new battery and caravan all should be well.
 

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