Been chasing what i think is a battery drain issue - I dont use the car daily, so the voltage slowly drops down to about 12.5 when asleep, unlocking the car (which pulls 15a) will pull the battery down to around 12.1 - 12.3 volts and it appears that anything less than 12v it will refuse to start.

I have replaced the starter (likely in error as i thought it was click of death) and has a new Bosch AGM battery (although i've not registered it)

I believe i'm just not using the car enough because I've fitted a battery monitor - which is pretty decent device as it keeps a log of all your starts and voltage history for many days and i can see it just slowly drops and the car is not repeatably waking up (as the volt drop would be very obvious on the logs)

Anyway last weekend I drove a 4 hour trip and when i arrived, I thought i bet the battery should be nicely charged - took a look at the history and was pretty surprised to see the battery had less volts than when i started the journey four hours earlier and the voltage all over the place. Wife also noticed her seat heater kept turning off, which I suspect it was doing so because the battery was getting low:


Sure enough, tried to start it the next day and the battery was too weak and luckily i eventually managed to get it started with my Sealey Electrostart 1600 (supercapacitor based)

Had mega anxiety for the journey back, but oddly it was solid all the way back with no fluctuations (stopped once for fuel at 14.00 on the graph)


To be honest I was expecting a 14.8v bulk charge and then perhaps it dropping to mid 13's as a float charge - but I dont actually know what is a "normal" charging profile. after the four hour return journey i checked the battery temp by hand and it was normal.

is this a failing alternator or maybe because the new battery hasn't been registered - does it make a significant difference to the charging profile. Are there any decent documents on the charging characteristics to do more troubleshooting.

This is the monitor - very good:
https://www.amazon.co.uk/dp/B08VHMJYXY?ref=ppx_pop_mob_ap_share

AGM battery will need registering to update the charging behaviour. 2012 TDV8 Vogue (L322)

Now it’s warmer, my AGM needs a slightly lower charging voltage…..14.4 to 14.6
Charging system on the 11s and 12s was not intended to fully charge the battery….but keep it over 80% charged only
On long runs, my charging voltage drops to 13.7

Excess drain from the battery is drain > 20mA

As JayGee says….the car needs telling a new battery has been fitted. Otherwise a higher voltage than necessary will be used, which may reduce battery life

I would check battery terminal connectors …..

Seems to be getting worse - at idle now it wont charge at-all. If you bring the revs up to about 1500rpm it will suddenly kick in.
I've still not managed to register the battery, but I'm not convinced that's the issue here. My friend did have the IID diagnostics for this car but he cant find the dongle - so i cant do any further troubleshooting.



This was driving the other day:

Click image to enlarge

Check the belt/alternator. Other things to check and fix would be earting and bad contacts.

Also consider this mod https://www.fullfatrr.com/forum/topic31909-75.html
You will significantly increase the "starting" headroom with this mod, and the car will start happly sub 12v.

Note: I have a drain issue much like yours( which i have to tackle at some point) but the car cranks very happly with low SOC SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

Mezo, I’m having exactly the same with mine, also using the same Bluetooth battery monitor. I’m not sure this is an issue as, despite it seeming like very abnormal behaviour, at no point has the battery warning light on the dash come on, which would be the point that the vehicle thinks there’s a problem. It still leaves me anxious to see the charge get so low, so am monitoring closely to see how it pans out. I have narrowed it down to be most likely either bad earthing points or a problem with the battery monitoring system (BMS). Here’s what I’ve done so far, all in the last 3 months:
- new AGM battery
- new Denso starter motor
- new alternator
- cleaned battery clamps
- cleaned battery -ve to chassis connection
- starter relay mod as linked above (this is highly recommended!)
- additional engine to chassis Earth strap

Despite all of this, my charging has been like yours. Sometimes it’s a solid 14v all journey, other times it’s all over the place. However, it does rise whenever under load or when coasting, then goes to 12.6 or less when cruising at low revs.

My next job is to clean the other Earth points linked to battery junction box and central junction box. If they fail, I might buy a new BMS cable as there’s an updated version available for about £110.

Let me know how you get on and I’ll do the same! 👍 Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!

Andy, I had the same issue before and have done all of the mods you have done plus a new BMS. Replacing the BMS did not help (bad BMS will show on the dash). My charging has improved(may be fixed), but I feel there is a persisting underlaying issue that will pop up again.

Next steps for me:
- Replace tensioner/etc
- Go through earthing completely. (It will be good to know all the earthing points for our model.


Starting mod is a "Fix"
Charging improved (may be a Fix also)
Drain is not fixed

pd SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

I think you're looking for a problem that doesn't exist, many manufacturers have used 'smart charge' systems for some time, where the voltage is lowered to reduce load on the engine - mainly for reduced emissions, it's not uncommon to see a system voltage of 12.6VDC with a battery at >70% SoC, provided the voltage rises when the battery is discharged, most commonly after repeated engine starts or the external temperature is low, then everything is OK.
The charge voltage is controlled via LIN to the generator from the ECM, not the old 'dumb' alternator regulator method. This is another reason to ensure the chemistry of the battery is the correct one for the vehicle as the charge strategy is different dependent upon battery type.
Lower 'float' charge voltages also help weith preventing cell sulphation, thereby extending the life of the battery.

Remember that the useful output of the generator is the Amps, the voltage is just the carrier.

ffrr14, really helpful as always! 👍

For all following this thread, I found another really useful thread a while back that explains how the BMS works in quite some detail here https://www.fullfatrr.com/forum/post612752...f34#612752

The key takeaway for me is that the BMS deliberately allows the battery to be discharged as a routine before charging back up again. When allowing discharge, it says it can go down to around 12.2V (but not lower). It also says that the re-charge cycle can take many days to complete if only short journeys are undertaken.

The interesting thing for me is that my observations of charge while driving and charge before starting seem to fit this model. I have to admit that it’s very alarming when I monitor the charge while driving, but I’m not seeing my battery below the (apparently) crucial 12.6V before attempting to start. When I unlock the car it does drop to about 12.35V but I have to put that down to the current draw from all the ECUs when the car is woken.

I will pause here for a couple of observations on the specific Bluetooth Battery Monitor that Mezo mentioned and that I also have. It’s an excellent purchase and so cheap, I highly highly recommend to all! I initially connected it to the battery +ve and -ve as told to do in the instructions. However, while researching the vehicle’s BMS on here I saw a few posts that mentioned that you shouldn’t connect things across the battery as it can upset the BMS. Examples include trickle chargers, jump start booster packs, and Bluetooth battery monitors like the one I have and mentioned by mezo. So, I decided to mount it elsewhere. I couldn’t find a good Earth point within reach of the battery +ve clamp without having to extend one of the Bluetooth battery monitor’s wires. I might do this as a future mod to keep it as close to the battery as possible but as an interim I’ve just put it in the boot in the driver’s side compartment. You can connect to the big red +ve feed from the battery and there’s plenty of bolts into the chassis structure there to find a suitable Earth. The +ve cable is always live as it’s fed directly from the battery so the Bluetooth battery monitor works fine; I just acknowledge that I’m probably losing up to a few tenths of a volt on the readings due to cable resistance. I might have got the risk of vehicle BMS interference wrong and am happy to stand corrected, but I didn’t want to take the risk of upsetting the vehicle’s BMS. Secondly, If you look at the graph on the images above, you only get a 5 minute snapshot of the voltage track. I was obsessing over this being so erratic and getting very anxious when driving as a result. However, instead of focussing on the snapshot, I’ve tried to step back and focus on the bigger picture. If you look at the longer term graphs in the app I can see that, whilst the V is erratic over the course of a drive, the post drive charge is still what I would want to see for a healthy battery.

As an example, I did a c.6 hr round-trip on Friday and below is a picture of my V graph for the whole 24hr period

You can see that before my drive the battery charge was approx 12.8, i.e. very healthy. During the drive you can see it vary quite a lot, from about 14.8 down to 12.2. Yes, there is one dip below 12.2 but I have ruled this out as a single instance and thus erroneous. The point is that it never went below 12.2. At the end of the drive, it’s a solid 12.6 again. My instinct is that after such a long drive it should be higher assuming good battery health. However, for now I’m happy to assume that this is the BMS doing it’s job.

mezo, you mention that on one occasion your vehicle wouldn’t start due to low voltage. Do you remember what the V was at the time? If you didn’t have a dash warning then I am highly suspicious that you have the same issue with your starter solenoid trigger wire that ffrr14 mentions in his post above. This wire is simply not up to the job of providing enough current to hold the solenoid open in anything other than perfect conditions. It’s a known and well documented issue and, I cannot recommend enough that you do the starter relay mod as described to fix this. If you do this mod, as ffrr14 says, you will have ample headroom to get the vehicle started, even in a low state of charge.

Going forward, the one thing we don’t know for sure is whether the behaviour being observed is normal for the BMS or not. I am slowly working my way around earthing and contact points to rule those out. However, what I feel we need is the wise words of an auto electrician who knows these vehicles well enough to rule in or out the observed behaviour as normal or abnormal for the BMS.

A long post I know, but I’m really keen for all to get as many facts and examples on the table as we can so we can get to the bottom of this potential issue. However, when all’s said and done and despite their unique personas, I still bl**dy love my L322! 😂 Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!

Jesus your charging profile is like mine - started at close to 13v and ended up less than when you started. I'm pretty sure that my car always went up to 14.7+ volts at idle until recently.
The clue that made me look the other day was the wife complaining that the seat heaters kept turning off.

I got the car up on ramps yesterday to consider pulling the alternator out - but I think i might hold off and get the IID diagnostics and examine the PWM commanded signal sent to the alternator as described in the workshop manual.

ffrr14 wrote:

Check the belt/alternator. Other things to check and fix would be earting and bad contacts.

Also consider this mod https://www.fullfatrr.com/forum/topic31909-75.html
You will significantly increase the "starting" headroom with this mod, and the car will start happly sub 12v.

Note: I have a drain issue much like yours( which i have to tackle at some point) but the car cranks very happly with low SOC

Phoenix wrote:

I think you're looking for a problem that doesn't exist, many manufacturers have used 'smart charge' systems for some time, where the voltage is lowered to reduce load on the engine - mainly for reduced emissions, it's not uncommon to see a system voltage of 12.6VDC with a battery at >70% SoC, provided the voltage rises when the battery is discharged, most commonly after repeated engine starts or the external temperature is low, then everything is OK.
The charge voltage is controlled via LIN to the generator from the ECM, not the old 'dumb' alternator regulator method. This is another reason to ensure the chemistry of the battery is the correct one for the vehicle as the charge strategy is different dependent upon battery type.
Lower 'float' charge voltages also help weith preventing cell sulphation, thereby extending the life of the battery.

Remember that the useful output of the generator is the Amps, the voltage is just the carrier.

Ajmngn wrote:

ffrr14, really helpful as always! 👍

mezo, you mention that on one occasion your vehicle wouldn’t start due to low voltage. Do you remember what the V was at the time? If you didn’t have a dash warning then I am highly suspicious that you have the same issue with your starter solenoid trigger wire that ffrr14 mentions in his post above. This wire is simply not up to the job of providing enough current to hold the solenoid open in anything other than perfect conditions. It’s a known and well documented issue and, I cannot recommend enough that you do the starter relay mod as described to fix this. If you do this mod, as ffrr14 says, you will have ample headroom to get the vehicle started, even in a low state of charge.

I am loving the mod and the car now. Anxiety around starting is gone now, and I am beginning to enjoy the finer things like HD sound wafting suspension and "the power" is mesmerising

I do understand the BMS function and logic, but I did have an issue where the charging was impacted as if something was loose in the engine bay and there was. I found a nut loose in the distribution box behind the battery.

I have cleaned and tightened all the connectors/nuts/fuses and the charging system is much happier and has fixed random issues like ACC going offline etc etc

On a separate note, I do feel the charging circuit/logic/profile is not consistent with the cranking demands. In the past (at times) the car would not start after few short trips, but would crank if allowed to cool down ..I couldn’t explain this tbh, but all that is gone with the mod …now on to the drain

pd SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

Mezo, I wholeheartedly agree with ffrr14 ref the starter mod. There’s other more detailed threads on here but to try and summarise (also acknowledging GraemeS’ contribution on this from a previous conversation I had with him):
- The red wire that goes from the engine fuse box to the starter solenoid is over 6m long. The first 3m are 4mm2 but it then drops to only 2.5mm2 for the last 3m. It’s a terrible design, and can’t provide enough power to hold the starter solenoid contacts closed whilst the starter motor cranks. This is the click you hear. As the wire ages or corrodes under the sheath, it builds up resistance and I’m convinced is the main cause of most starting issues on the TDV8 engines.
- You can do a simple mod of replacing this wire with a new shorter one, preferably at least 4 if not 6mm2. Either cut into the loom, or find a way of using a new connector so you can leave the loom untouched and replace the wire in the plastic plug in the fuse box itself. This will technically do the job but may not be up to the job over time, or in suboptimal starting conditions.
- the optimal solution is to wire in the separate relay as GraemeS, ffrr14 and I have. There’s different ways of doing it, but they all have the same outcome. Red trigger wire feeds 12V to relay switch instead of starter solenoid - relay switch enables 12v feed directly from battery to starter solenoid over much beefier cable. If this doesn’t hold a starter solenoid closed, even in the worst conditions, nothing will.

I would advise you to separate the no start issue from your potential charging issue. If you improve the wire to the starter solenoid with either method as described, you’ll almost certainly get a guaranteed start unless you have a genuine issue with a component. You’ll also have zero anxiety over whether you’ll start or not. Once done, we can all keep comparing notes on charging to see whether the behaviour is normal or if there is still another issue! Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!