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Discussion Starter · #1 ·
Hi all,

I'm having issues with the batteries on my LR DS MHEV 2021.

Bought car new in March 2021.
Often getting 'please start engine battery low' messages.
First call out to flat battery in early July 2021
Many fails since then, I think we are on 4th new battery. Been into JLR dealership twice for over two weeks both times.
Failed again last week after a software update overnight. Next morning flat battery and can't get into car.

I tow and the tow bar is not JLR but the wiring loom is, not fitted by JLR. JLR are saying this might be what's causing it - but the issues do not always happen after I've been towing - only the once was the car totally dead after towing. All others either after software download or just out of the blue.

Any thoughts? Anyone with similar?

Julia.
 

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Sounds like a parasitic draw and usually on newer vehicles it's because a module isn't going to sleep. The usual diagnostic procedure is to trick the car into thinking the doors are closed (so you can get to the fuses without waking the car up), hook an ammeter up in series with the battery, wait for the car to go to sleep which could take a while. I haven't checked how long mine takes to go to sleep but seems like at least 10 minutes. If you have more than about 20 milliamps of draw on the battery it's probably too much. Then you check voltage drop across all the fuses until you find the one (or ones) with voltage drop, which indicates current is flowing across that fuse. Figure out what that fuse feeds and go from there. Usually you can unplug modules until you find the one that stops the current draw and the usual fix is a new module if you find a bad one.

If you search youtube for parasitic draw you'll find some good videos on how to track them down. If you see anything from South Main Auto, Pine Hollow Auto Diagnostics, or Scanner Danner, those are all pretty good.
 

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Discussion Starter · #3 ·
Sounds like a parasitic draw and usually on newer vehicles it's because a module isn't going to sleep. The usual diagnostic procedure is to trick the car into thinking the doors are closed (so you can get to the fuses without waking the car up), hook an ammeter up in series with the battery, wait for the car to go to sleep which could take a while. I haven't checked how long mine takes to go to sleep but seems like at least 10 minutes. If you have more than about 20 milliamps of draw on the battery it's probably too much. Then you check voltage drop across all the fuses until you find the one (or ones) with voltage drop, which indicates current is flowing across that fuse. Figure out what that fuse feeds and go from there. Usually you can unplug modules until you find the one that stops the current draw and the usual fix is a new module if you find a bad one.

If you search youtube for parasitic draw you'll find some good videos on how to track them down. If you see anything from South Main Auto, Pine Hollow Auto Diagnostics, or Scanner Danner, those are all pretty good.
Thank you for all this. I would have thought main dealer who have had it in twice now for work (first time two weeks, second time three weeks) would have checked this but I can ask the question this time.

I've left the car hitched up now since last Sunday and the car is still ok - no dead battery so how can it be the trailer electrics, that would have been long enough to drain the battery if it was I would have thought?!
 

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I've left the car hitched up now since last Sunday and the car is still ok - no dead battery so how can it be the trailer electrics, that would have been long enough to drain the battery if it was I would have thought?!
All kinds of things are possible. Could be an intermittent issue and it's not acting up right now. That makes diagnosing the problem extra fun since they have to also figure out what causes the fault to happen if it's not happening at the moment they look at it. A lot of dealers / mechanics will avoid spending hours of time trying to chase down an intermittent issue and that's mainly because their customers don't want to pay $500 to hear they couldn't find a problem. It could be that having the trailer electrics hooked up actually makes the tow module behave correctly and go to sleep and when it's unhooked you have the battery drain. But it's just as likely something else.
 
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