Discovery 4 2015 auxiliary battery Question

Hello all,
can anyone shed some light on this issue I’ve had for about 5 years.
I have a 2015 discovery, I had down in France in 2018 and she sat out in the snow for a week whilst I was up in the mountains.
When i came back and started her up the eco/stop start was illuminated on the dash saying not available, didn’t bother me as I’m not bothered but the stop start feature.
What also did happen then I believe was the small auxiliary battery went tits up as the interior lights or radio won’t stay on for more than a few minutes if the engine is not running.
Anyway I changed that battery and ever since then I still get this message on the radio screen saying battery low start car if I’m sitting in the car with engine off and the radio or interior light is on, it’s says system will shut down in 3 mins if engine isn’t started.
The car main battery is new and I’ve disconnected the small battery and tested it with that fluke meter and it’s holding about 13 odd volts so that small battery is getting charged.
I’ve had a new alternator put on her last year and the guys put a new gateway ( whatever that does)to see if that would help but no joy.
Start stop still don’t work ether.
Any help much appreciated.
Thanks

Its more likely to be the starter battery or the BMS, the auxiliary battery in autostop configuration doesn't get a lot of use.
Did you get both BMS reset when the batteries were replaced?

Graculus said:

Its more likely to be the starter battery or the BMS, the auxiliary battery in autostop configuration doesn't get a lot of use.
Did you get both BMS reset when the batteries were replaced?

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Thanks for your reply I’m not aware that the BMS has been reset, wasn’t even aware of it until I’ve started reading a few other posts, I’ll ask the guys at my local garage to reset it.
Thanks.
Graham

If you didn't reset the bms when changing batteries you proberly cooked your new batteries

Not necessarily - if the BMS detects a low battery capacity or high internal resistance it will signal the ECM via the GWM to limit charge voltage.
The BMS will recognise improved internal resistance but not capacity, so the GWM will therefore initiate warning messages & signal the quiescent current control module to shutdown as the voltage (and therefore charge level) drops. Unless the BMS is 'aware' of the improved battery capacity, the GWM will initiate an early shutdown to preserve the ability to start the vehicle.
It does remind me to ask - are the replacement batteries fitted of the correct type? they should be AGM and autostop rated. - was the GWM 'new' and configured to VIN or was it a used item and just plugged in?

Graculus said:

Not necessarily - if the BMS detects a low battery capacity or high internal resistance it will signal the ECM via the GWM to limit charge voltage.
The BMS will recognise improved internal resistance but not capacity, so the GWM will therefore initiate warning messages & signal the quiescent current control module to shutdown as the voltage (and therefore charge level) drops. Unless the BMS is 'aware' of the improved battery capacity, the GWM will initiate an early shutdown to preserve the ability to start the vehicle.
It does remind me to ask - are the replacement batteries fitted of the correct type? they should be AGM and autostop rated. - was the GWM 'new' and configured to VIN or was it a used item and just plugged in?

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Thanks again for you help G,
The batteries are both the same as Landrover spec, when they tried the gateway I’m not sure if it was one they had in the shop that they use for testing or it was a new item, they put my original back after as it didn’t make any difference. I’m going to pop over today and ask them to do a BMS reset and I’ll also ask them if they configured the gateway to my vin.
Hopeful this may help, having no interior lights in the evening is becoming a real ball ache as my eyes are on there way out also because of my age
Thanks,
Graham

Brodsord said:

Thanks again for you help G,
The batteries are both the same as Landrover spec, when they tried the gateway I’m not sure if it was one they had in the shop that they use for testing or it was a new item, they put my original back after as it didn’t make any difference. I’m going to pop over today and ask them to do a BMS reset and I’ll also ask them if they configured the gateway to my vin.
Hopeful this may help, having no interior lights in the evening is becoming a real ball ache as my eyes are on there way out also because of my age
Thanks,
Graham

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Interior lights, tried pushing and keeping pushed the centre of the three lights?
Same to turn them off full time.

lynall said:

Interior lights, tried pushing and keeping pushed the centre of the three lights?
Same to turn them off full time.

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Hi yeah I’ve tired that they don’t come on unfortunately.
If I’ve been on a longish journey, when I stop I’ll probably get about a minute or so of the interior lights then then go out, if I’m going to do a bit of shopping at supermarket for instance locally, when I come home I’m in the dark getting bags out of car, I live in the sticks and my drive is pitch black.
this fault hasn’t really bothered me up until my eyes have started playing up

Brodsord said:

when I stop I’ll probably get about a minute or so of the interior lights then then go out,

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If you let one door(any door) open and you lock with the fob do you get an audible misslock warning? if not it's possible that a door switch failed and the CCU "thinks" that a door is open and the interior lamps are on that mode which is reset only by turning the ignition off and on... if you get misslock warning forget about this

Brodsord said:

Hi yeah I’ve tired that they don’t come on unfortunately.
If I’ve been on a longish journey, when I stop I’ll probably get about a minute or so of the interior lights then then go out, if I’m going to do a bit of shopping at supermarket for instance locally, when I come home I’m in the dark getting bags out of car, I live in the sticks and my drive is pitch black.
this fault hasn’t really bothered me up until my eyes have started playing up

Click to expand...

Its possible the BMS is faulty, even without a reset it should be providing 'comfort' power longer than you state. Are you aware of the vehicle being jump started at all? If so, was the negative (ground) lead connected directly to the battery terminal? If it was, or there's a possibility it was, then its likely the BMS needs replacing. When you take it in, ask them to read the stored data from the BMS and compare to actual values, that should give you an idea if the BMS data is accurate. Also get them to read current draw, with the ignition off and no BSU connected, then with a BSU connected, it should initially be less than 10A draw and go to a positive figure with the BSU connected.