I'm after some advice and guidance from you knowledgeable folk please.

In colder weather, my vehicle operates perfectly without any hiccups and i can drive up and down the country with no issues. However, as the outside temperature rises and things heat up, I'm encountering a consistent problem with power loss in terms of battery power in that I then get the Christmas tree light effect on the dash. This manifests as battery discharge and the appearance of various warning lights on the dashboard, leading to frustrating situations where I've been stranded due to limp mode, gearbox error messages, HDC error messages, low battery issues, etc.

To provide some context, I've recently replaced both the main and the Aux batteries with brand-new ones, and I've had them tested - they hold a charge and are in good condition. Given this, I'm starting to suspect that the root cause might be related to the alternator not effectively charging the batteries in hotter conditions.

Has anyone else faced a similar problem? I would greatly appreciate any insights or suggestions you might have regarding the potential causes of this power loss in hot weather. Is it likely an alternator issue, or could there be other contributing factors?

Thank you all for your time and assistance. 2016 Range Rover L405 4.4 SDV8 Autobiography

Does your vehicle require the battery monitor to be reset when a new battery is fitted? If the battery monitor thinks that the battery is original then it will keep the charge rate lower than for a new battery.

Have you monitored and compared voltages and currents on cooler and warmer days?

Hi Graeme, Thanks for your reply. Yes, I reset the BMS when the new batteries were installed. In the hot weather, the alternator still seems to be putting out between 13.7 - 14.2 volts, so it just seems very odd and frustrating at the moment that this only happens in hot weather. 2016 Range Rover L405 4.4 SDV8 Autobiography

As battery charge rate is reduced in hot weather to protect the batteries, perhaps the particular temperature sensor is faulty. If you have a diagnostic tool then maybe see if you can find a temperature sensor related to the BMS or charging to monitor.

It ended up being the BMS that would simply stop working and communicating with the ECM to send through signals to charge to the alternator in hot weather following diagnostics, so a new one has been ordered which will hopefully solve the issue (Fingers crossed). Thats what has been explained to me anyway 2016 Range Rover L405 4.4 SDV8 Autobiography

Could it be that in hot weather you are using the AC, maybe a fault on that system? 2018 SE SDV8 4.4 Byron Blue

Thanks Kot, I'm going to give the new BMS a try and see if that provides resolution and then if not, you have a point over the aircon 2016 Range Rover L405 4.4 SDV8 Autobiography

My sister has pretty much been having the same problem as you have described ,numerous times in the garage until finally they tracked down in the hot weather a faulty earth strap a new one fitted and touch wood has been fine for the last 3 weeks
The garage reckoned there must have been a break in it somewhere and due to expansion in the heat it kept tripping the car out

I was going to say check earthing straps

You guys were indeed correct. After checking the earth on the negative battery lead and also the driver's side wheel well, the nut had snapped off the earth connection meaning the earth on the negative lead was loose and not touching the chassis correctly hence i think my intermittent issues in the heat. Thanks for all the help and advice that was very much appreciated and also went against the professional advice i had over the BMS. 2016 Range Rover L405 4.4 SDV8 Autobiography

Glad it was of help and hopefully sorts your issuses out