Hi all,
Does anyone know what would cause a battery drain on the main battery but not the auxiliary battery?
( I thought they were both connected)
The Auxiliary is reading 12.5v which is fine,
The Main battery reading 12v after a week of being left. (Brand new main battery).
Many thanks.

I'm assuming you're the same as me with a non stop/start two battery set up where the auxillary is called on when necessary but is not normally connected in parallel.

From the workshop manual:
The dual battery system on non-stop/start system vehicles assists the primary battery with engine starting under certain ambient and electrical conditions.
The dual battery system uses the auxiliary battery which is switched in parallel with the primary battery if the ambient temperature falls below a certain threshold, or the state of charge of the primary battery falls below a certain level. The function of the auxiliary battery is to assist the primary battery in cranking the car at a suitable speed to provide a start Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

I'm not an expert but as you know I also think I have a problem though not as fast a drain as yours.

A few random thoughts:

You may have a faulty new battery.
You may have something draining it.
There is no information on likely or tracing L405 drains that I can find but plenty on the L322 fora on how to go about tracing one.
Suggest you have a search and a read.
Or call in an autoelectrician.
If you get as far as checking individual fuses, the glovebox fusebox is not easy to access and I wasn't sure what to remove to access the engine bay one. I still plan to check through the boot fuseboxes when I get around to it. From reading around I found the fuses don't need to be removed as each fuse has a known impedence and you can measure the voltage drop across it and then calculate the current flowing through it.

Sorry can't be more help. Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

Thanks for that!
I’ve decided to let my local LR specialist deal with it and source the drain.
Hopefully isn’t too costly and estimated 2-4hrs labour to find it. Obviously this is a bit unknown time frame!
Knowing what they charge per hour hopefully it doesn’t run over this!!

Did you get anywhere with this? Be interesting to know if there is a common culprit. Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

It’s going into my LR specialist in a couple of weeks will keep you updated! 🤞🏻

Is this causing any issues on your car Max?

My main battery seems to hover between 12 and 12.5v.

No faults except auto stop/start doesn't seem to function (2016 4.4SDV8 so I have it)

I did charge the car via the posts under the bonnet (I believe this only charges the main battery?)

Don't want to buy a new main battery if it isn't really needed.

I just have to charge it at least once a week otherwise battery drops bellow 12v and don’t want to start damaging the new battery or other modules in the car. Mine is a 2013 so doesn’t have stop/start luckily!

12.1V is about the lowest you should let an AGM battery go to avoid damage.

Lack of stop/start is probably caused by low battery

Yes, engine bay posts only charge the main battery, in my year anyway. Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

Max,

If it’s not your primary vehicle, you could try disconnecting the battery negative and monitoring it (as though it were out of the vehicle) to see if it retains charge over several days?
Probs not worth it if it’s booked in tho’.

Good luck!

How’s your tailgate operating? “If it ain’t broke, don’t fix it” -where’s the fun in that?

I fitted a brand new battery so can rule that out!
Thanks anyway!
Hoping the garage is source it getting fed up with sticking it on charge once a week!
Luckily my tow bar electrics have the permanent battery live so have a ctek charger with a trailer socket on the end for quick connection! Saves taking the battery out or opening the bonnet up!

Tailgate operates fine without any issue.
I’ve noticed my front passengers door the soft close feature doesn’t work, but all the other doors work fine. Perhaps that door module draining the battery?
Don’t want to start spectating could be anything!

Hmmm, is it draining, or simply just not charging?
Once the SOC drops below a certain value, you will get various Gremlins
A specialist auto electrican will be more use usually than the main dealer, in my experience. “If it ain’t broke, don’t fix it” -where’s the fun in that?

It’s draining. I fully charge it to 12.8v. Over a week it will discharge down to 12v.
I would never use a main dealer.
Going in to my local LR specialist who are very good!

Mine was doing similar Max, main battery was dropping to around 12 to 12.4v.

Tested by a trusted mechanic using a midtronics tester unit which came up with replace battery.

I went out and sourced my own replacement.

Only thing that wasn't working on mine was the aforementioned stop start (I understand you don't have this)

It would work when I charged the main battery but only for a couple days.

Day 1 today running with the new main battery and stop start is working.

It's likely your also headed for a new main battery from the sounds of things