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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Battery Drain Help Please
Hi. This is my first post and hope you guys may be able to help out. I love my Defender but would admit to not being overly mechanically minded. I have been having battery issues for a couple of years now. I barely get 12 months out of a Yuasa 12V 110ah battery. I admit to doing a lot of short journeys but do do longer runs too and have a trickle charger which I use now again to try and maintain battery health.

I searched online and found a post of Defender2.net which sounded very similar to my issues. I've pasted it below. I did try Direct messaging the chap (tong.g) who posted it to see if he ever found a solution but as a new member I'm not allowed to DM just yet.
I apologise in advance if copying messages is against the forum rules.

My battery was showing 13.03 on a multimeter yesterday evening. It started perfectly this morning and I drove to work. Got in to come home and nothing doing. Not even a light on the dash!

Anyway, any thought?

Here is what tony.g posted a few years ago but I have no idea if he ever resolved his issue and how it was done if he did!

Thanks

Have an ongoing but intermittent problem with battery drain. Replaced the alternator incase the diodes were faulty, but no change. Also got new battery.
Took it into dealers for check and they had it over two nights but their results show no abnormal battery discharge - just clock and immobilizer etc.
Had it back and OK over one night, but went to start it again this evening (after standing approx 30 hours) and battery completely flat, not even ignition lights would come on. There must be something heavy using up the current but can't find anything - everything switched off and key removed. I don't even set the alarm as it's always left overnight in a locked garage.
Getting desparate now and any pointers/suggestions would be welcome.
Post #1077488 14th Oct 2025 6:49pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 6054
2006 Defender 110 Td5 USW Zermatt Silver
In my experience.


It’s always something that has been “done” “altered” by others.

Has yours got alterations, modifications that have involved the electrical system?

I would get yourself a good multimeter, and see what you are drawing from the system then start to remove fuses, and things from the system.
Post #1077492 14th Oct 2025 7:01pm
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Hi.

Thanks for the advice. It has what I assume is a factory fitted alarm. There is a redundant CD changer which until fairly recently I didn't even know was there/what it was. I did have a radio installed but a few years ago.

I'll give the multimeter a go and see what I get.

Cheers
Post #1077495 14th Oct 2025 7:05pm
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revd



Member Since: 20 Apr 2024
Location: England
Posts: 295
United Kingdom 
must be a heavy draw - and not all circuits are fused. I can run an Engels fridge overnight without issue. Until the problem is solved it would be worth fitting a battery disconnect/isolator switch
Post #1077508 14th Oct 2025 8:36pm
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Thanks for the advice about getting an isolator. Would you have a hunch what it might be?
Post #1077510 14th Oct 2025 8:52pm
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revd



Member Since: 20 Apr 2024
Location: England
Posts: 295
United Kingdom 
No idea - I would start with the easy stuff, pull fuses and relays one at a time over night, check light switch/ignition switch/wipers and heated rear screen.
Post #1077519 14th Oct 2025 9:42pm
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Ok. Thanks for your help
Post #1077521 14th Oct 2025 9:51pm
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leolito



Member Since: 07 Jul 2025
Location: Sofia
Posts: 38
Bulgaria 
The advice above is the way to go.
Bear in mind if you started up overnight without issues and it "died" after a few hours in the day, assuming you have a healthy battery, then it is indeed as mentioned a heavy draw, a 110Ah battery in good condition should be able to "deliver" up to 110A in one hour, that is a lot ...

If you are good with the tester, you can measure as indicate "leftover" drain once all systems are off.
Put it on A and if you see anything bigger than a few mA then you got a system that is left "on".
Keep particularly an eye on the alarm, actually trace the cables if is aftermarket it will show and it might have a fuse there - you can remove it if so, to eliminate one area of concern.

If you find 13.03V on the battery before startup I would not be concerned with self-discharging, should be OK.
Is the radio powering off when you switch off ignition? You can check that as well.

Very Happy
Post #1077547 15th Oct 2025 8:18am
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revd



Member Since: 20 Apr 2024
Location: England
Posts: 295
United Kingdom 
My main concern with that amount of discharge is something might be getting hot, and consequently increasing the risk of a fire
Post #1077555 15th Oct 2025 10:22am
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Mr.Jimbo



Member Since: 20 Jun 2024
Location: Rugby UK
Posts: 36
United Kingdom 2003 Defender 110 Td5 CSW Java Black
Have you had the battery tested? I only ask as I had a similar sized Yuasa fail recently - it would charge up on my CTEK just fine, and when freshly charged would start and run OK - however it would die well within a week, and when I returned it to Halfords they diagnosed a dead cell straight away and it was replaced. Battery was at most 18 months old.

I was chasing a similar train of thought but couldn't find any significant drains beyond the clock and alarm etc. 2003 TD5 110 CSW
Instagram: e12_hue
Post #1077575 15th Oct 2025 11:47am
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Thank you al for the ideas of things to try to help resolve my problem. I'll get testing as soon as I can over the weekend.
Post #1077628 15th Oct 2025 9:01pm
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AMBxx



Member Since: 24 Jul 2016
Location: York
Posts: 1071
United Kingdom 2015 Defender 110 Puma 2.2 XS CSW Orkney Grey
revd wrote:
No idea - I would start with the easy stuff, pull fuses and relays one at a time over night, check light switch/ignition switch/wipers and heated rear screen.


Asking out of ignorance here - why wouldn't you just use a multi-meter to test the current draw from the battery rather than keep leaving overnight?
Post #1077670 16th Oct 2025 10:34am
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
Hi

Managed to do a multimeter test and saw a drop when the alarm system 15 amp fuse was pulled out. It's in the fuse box under the drivers seat. As far as I'm aware it's the factory fitted alarm. Any thoughts from anyone?

I've attached a picture of the back of the fob I use to arm the system if it's any help

Thanks

Click image to enlarge
Post #1078182 23rd Oct 2025 6:37pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 6054
2006 Defender 110 Td5 USW Zermatt Silver
Looks like a standard LR fob, and would be surprised if that was the culprit.

What figures are you seeing, and how are you testing.
Post #1078185 23rd Oct 2025 7:50pm
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MrMustard



Member Since: 11 Oct 2025
Location: Worcestershire
Posts: 7
United Kingdom 2001 Defender 90 Td5 CSW Barolo Black
I was using a multimeter which I think my friend who was helping me had set on 200ma setting. It was reading 0.6 until the 15A alarm fuse was pulled when it dropped to 0.2. It was the only fuse once removed that caused the reading to drop
Post #1078201 23rd Oct 2025 9:41pm
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