Replaced my main battery recently as I had an almost permanent low battery warning and the old one wasn't holding charge even when not connected.

Been monitoring the new one with a BM2 as voltage is dropping rather too fast for my liking. Midnight to midnight yesterday it dropped from 12.68 to 12.46, although that was a little more than usual. I ran some tests last week and seem to have a consistent drain of around 80mA when asleep whether locked or unlocked. According to the workshop manual it should be under 20mA. Does this drain seem consistent with that sort of voltage drop?

There doesn't seem to be much on the forum re drains on the L405 so any usual suspects or do I just plough through the fuse boxes? I've already ruled out my dashcam, the BM2 itself and auxillary battery is good. 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

Any update to this?
Even after fitting a new main battery, I have to charge my l405 once a week if it’s not used or I get low battery messege!

Just a thought: if the aux battery is knackered, could it cause a drain on the main battery, perhaps?
Might be worth checking the aux battery behind the R/H side panel in the boot for SOH. “If it ain’t broke, don’t fix it” -where’s the fun in that?

Max94L405 wrote:

Any update to this?

I see nothing wrong with those voltages given the low ambient temperatures and the time scale, how are you measuring the 80mA? is that an average, peak or constant?

Thanks for the advice on what to expect. So 9 days for 12.8 to 12.2 is acceptable? The problem is I don't know what I should expect hence my initial post.

The 'around 80mA' is a visual average i.e. the display was fluctuating between 70/80/90. 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

The display on what?
To be honest, with a display resolution of 10mA, whatever you're using isn't going to be that accurate, quiescent current is best measured using an in-line ammeter or datalogger, clamp ammeters on DC are not the best for low current and do drift over time - unless you want to spend a lot more than it'd cost to have it checked by a specialist.

Presumably you had the BMS reset when the battery was changed? do you still get the low battery warnings? What is your usage pattern like? - journey time, type of journey (commuting/open road/local short journeys etc.) time of day etc.

I use a cheap multimeter connected inline between the battery negative post and the clamp. I realise it isn't going to be that accurate but there is a lot of difference between the workshop manual <20mA and my readings of 70-90mA hence my belief that I have more drain than I should have.

Yes, BMS was reset. I haven't had a low battery warning with the new battery because the car has been used a bit more recently so voltage ahsn't dropped below about 12.4V

I have been monitoring the voltage so I know what to expect when I don't use it for many days as has been the case over the last 9 days. As I said in my first post today, it has dropped from 12.8V to 12.2V over that period, so if that is reasonable and/or to be expected then I can live with it.

Unfortunately there seems to be no data or even opinions on the forum as to how long a L405 should last from charged battery to a point at which it should be charged. 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

Any vehicle should be capable of being parked up, undisturbed for two weeks - as long as the starter battery is >80% charged to begin with. Not specific to JLR but we get a lot of issues with people 'checking in' with their vehicle - some sort of automotive separation anxiety I think. This causes the Telematics to wake up all the body modules and of course the gateway, this only lasts for ~30 mins before the current drain is back to expected levels but when this happens 3 or 4 times a day whilst the driver is on hols, it can cause a non-start condition, even though the battery is healthy.
Rightly or wrongly, the JLR implementation of the BMS on the L405 means the battery SoC will always be around 80% of capacity, this will always give a lower than convention dictates terminal voltage due to standing time and/or ambient temperature.

Honestly, I don't think you have a problem with the vehicle, possibly an issue with data collection and over-analysing it - I wouldn't trust anything that starts with the descriptor 'cheap' to give reliable data.
Also bear in mind that it can take >30 mins to get down to 20mA current draw, and there will be periodic spikes above that, it's generally accepted that anything below 40mA is 'OK' after the full shutdown period, this varies between vehicles but in general, anything measured in the first hour can be discounted. We always run a minimum of a 12 hour check, usually more like 15 or 16 using a calibrated datalogger, a multimeter is fine if it is reliable and accurate. If you're going to focus on current draw, then you really need accurate and reliable measurements and a long sampling period.

Short answer - if you're not experiencing any issues, then everything is fine.

Long answer - full analysis of battery SoC depends upon a lot of factors, usage having the biggest effect, battery type, temperature and battery quality all have an impact upon SoC, measurement of voltage and current needs to be accurate and over a long period of time, snapshots are useless.

@Phoenix:

QED as they say,

I can testify to the anxiety part -our last vehicle before the FFRR was an Evoque HSE, an ex demo vehicle fully loaded with every conceivable option including the 850W audio, and due to short trips and loud music, we got “battery low, please start engine” almost on a daily basis, so we got a CTEK MXS-5 and the issue disappeared literally overnight. Move on a few years, and we got the full fat. Lo and behold, within a few weeks of ownership, similar issues arose, and even with the CTEK attached nightly, the tailgate became sluggish, and satnav updates became impossible, so we fitted a new battery, and all was well, however, due to historical/hysterical anxiety, we STILL plug the CTEK in nightly!  “If it ain’t broke, don’t fix it” -where’s the fun in that?

There is a lot of usage data that is recorded by the vehicle, I don't have any to hand but I'll add some anonymised screenshots to give an idea of parameters that are monitored by the vehicle systems - typically the concern is 'autostop not working' - actually, it is - it's preventing the engine from stopping due to low battery SoC, therefore it is working as intended, sometimes a difficult one to get across....

Thanks for your comphrehensive reply which is somewhat reassuring although I'm not sure that mine would last two weeks given that these have AGM batteries which I don't want to damage and that I'm almost down to 12V after 9 days. Batteries are cheap in the grand scheme of RR ownership but i see no reason to squander them unnecessarily.

I'm aware of the effect of waking the car up, in my case by doing unnecessary double lock presses on the remote occasionally due to car theft paranoia, which causes a voltage dip which the battery doesn't quite recover from, so mine has been completely 'untouched' for the last 9 days.

I did leave the multimeter in place for 24 hours perched on the parcel shelf and checked the reading periodically, which is where my base reading of 70-90mA is from. I also had the bedroom window open all night in case anything went wrong and triggered the alarm!

I shall check the rear fuseboxes for anything untoward but other than that monitor it and live with it. 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

Have a look at this, https://learnmetrics.com/agm-battery-volta...y-voltage/ it's not 100% correct but it's near enough - for a start, 13VDC is effectively 'surface charge' you'll never see that in reality - except in a very few minutes after switching the engine off. 11.8VDC will start the engine, even 11.0VDC 'might', dependent upon temperature. They also state that 10.5VDC is 0% charge, well, it does mean there's 0% above minimum voltage, but it's definitely not 0% charge.

As above, if there is no issue, then don't worry about the spot measurements.

ETA - if the meter was on the parcel shelf, did you have really long test leads or were you measuring just the current draw at the rear fuse box?
Most multimeters shut off after a few minutes, how did you restart it without 'waking' the vehicle?

Never had a problem starting even on my previous battery with almost permanent low battery warning because the auxillary battery is called on to help starting if necessary (this is a non stop/start V8 ).

Long leads used as meter needs to be close to the glass to be readable.

Meter doesn't auto shut off. Had already tested it to make sure it would stay on for 24 hours because if it did shutdown I assume it would trigger the alarm for a 'battery disconnected while locked' situation. 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