thanks - as it sits in the garage now it wont start again, so i'm going to try and measure the volt drop across the length of the wire.
As you said - i may or may not have two issues, non start and charging - the volt drop over the cable is easy enough to prove.

I've done the starter solenoid mod and posted updated photos of my approach on the other thread:
https://www.fullfatrr.com/forum/topic31909-75.html

Got the battery down to 12v and it still started fine. The original lead had 0.2 ohms resistance - the 50A lead is in parallel the original.

Click image to enlarge

So, this evening I took my battery out and cleaned all of the contact points in the battery bay with emery paper, wire brush and some contact cleaner. I also blasted all the push fit plugs in there with contact cleaner too (2 big ones on ECU, plus the BMS one on battery -ve terminal), then disconnected and reconnected each plug a few times to clean the surfaces. I was surprised how much corrosion was on some of the contacts, especially the copper ones in the junction boxes behind the battery.

Once done, I started the car 4 times in relatively quick succession and left to idle for a few minutes before switching off then restarting. Charging current was a steady and healthy 14.5 when idling, unlike the erratic readings the last time the car was used. I’m not drawing any conclusions yet as need to run it for a few weeks to observe and I have a few long 90 min drives coming up this weekend so will monitor the charging behaviour closely. I’m hopeful that, if there’s an issue, cleaning all of the relevant circuits and earth points will help eradicate it as ffrr14 has found. I don’t believe I have a battery drain issue but and still really keen to understand what ‘normal’ and ‘abnormal’ charging behaviour looks like to determine if I have a problem or not. 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!

What did you find? Any pictures? Also consider replacing the relays in the engine bay and for the air compressor. SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

Sadly not mate. I was trying to get as much done as I could before it went dark and, seeing as I’d bothered to get the battery out, I figured just to do as much as I could in there with the time I had whilst I could still see what I was doing.

However, a few observations:
- 400A mega fuse and mount that’s part of the +ve battery clamp assembly was pretty corroded*
- Same detail with *corrosion for junction box with the two 250A mega fuses behind the battery, especially the copper components; steel posts and nuts seemed to be clean in comparison. All bolts were tight and secure before cleaning.
- Junction box with numerous fuses also behind battery (the one with about 8 or so midi fuses) seemed a bit cleaner, maybe because more zinc plating over the copper than the mega fuse connections. Also, all bolts were tight and secure.
- male-female plugs on ECU and BMS all seemed fine but obviously very hard to tell condition where I couldn’t see. All I did with these was give a good blast from contact cleaner, leave for min 5 mins or so, then open/close plug multiple times to encourage good contact between metal parts in plug.

Next steps will be:
- observe for next few weeks to see if battery charging numbers raise or at least become more consistent with a higher charging V during a drive.
- continue contact/relay/fuse/ground cleaning in engine fuse box and central junction box (and possibly beyond).

I’ve an hour each way drive tomorrow, then a 90 min each way drive over the weekend to monitor charging behaviour. I’ll report back and hopefully post the graphs from my cheap and nasty Bluetooth battery monitor to compare from pre-cleaning. Obviously not going to be as good as high-spec kit under laboratory conditions but it’s all I got so better than guessing!

*I'm not sure if corroded is the correct word but, it’s what I’m using to describe ageing, dull, unclean, surface with deposits etc etc. 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!

Thank you, do share your findings. SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

Ok, an update on charging behaviours after a day of using the car for a few long journeys. I did two long runs this morning about 45 mins each way, plus a few other short journeys afterwards running some errands. I then did another long journey of an hour this eve. Graph from the day is below.

I kept the Battery Monitor app open for most of the driving and it was a solid 14.4-14.8 the whole time. I also started the day with the battery on 12.5 and finished at 12.9. Exactly what I’d want to see.

I’m not making any conclusions from this as I will continue to monitor over a longer period - this is just one day or driving being compared to another day of driving. However, there are now two working hypotheses:
1. Last weeks erratic charging that let you a lower battery voltage than when I started and today’s consistent charging leaving me with 12.9V is normal behaviour. The system is managing itself within stated parameters and, as there are no faults showing, no battery warning light on dash, and no worries about getting the car started with close to 12V, there’s nothing to do other than monitor charge and see if it affects other systems, e.g. mezo’s heated seats turning off.
2. My session in the battery bay cleaning contact points on cables, posts and fuses, and also contact cleaning the plugs on ECU, BMS etc, have done some good and now the system is getting more consistent readings and feedback. And it is this that is encouraging a more consistent charge behaviour.

I’ll keep an eye on this over the next few weeks as more long journeys coming up and will report back. I’d be interested to see others’ charging logs if you have them? 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!

3 Month update;
So the graphs I posted of the charge rate all over the place appears to be normal behavior - i've done multiple multi hour journeys with the same data.
So really, the actual issue was the weak cable to the starter solenoid causing it not to start with even a modest battery charge - I've had no starting issues at-all since, so thanks to the poster(s) who pointed that out.

I can also confirm that the erratic charging profile seems to be normal behaviour as within parameters as stated in the WM. I’ve added a screenshot of a typical day with multiple long journeys. You can see the charging V mostly in the mid-13s with occasional peaks up to 14V. Note, this graph shows data that is from a snapshot every 2 mins so is not a ‘constant view’. You can also see the third journey has much lower and more erratic voltages which is good example of why it was worrying. However, you will also see that when the car is parked, the V available is always about 12.5V which is both expected and ample to start the car.

There does seems to be 0.1-0.2V error (lower reading) between what I read on the Bluetooth BM or my cigarette lighter socket volt display and the actual V in the car as observed on my Gap IID live values. However, the car battery always seems to be charged to about 12.5-12.9 by the end of a journey and has never failed to start once since I did my starter relay mod with the better cable and additional relay from the battery 12V feed straight to the starter solenoid. I don’t doubt that improving the existing cable is also a great option but I prefer my over-engineered solution as it’s the best possible method for getting max V to the starter solenoid in all conditions.

Anyway, now that I have confirmed (in my opinion) that the BMS is working correctly and applying the right charge at the right time, this has now opened up another set of questions I have regarding auxiliary/leisure batteries and the split charge relays that control charge to them. I have read the specs for the relays and most seem to trigger the connection to allow the power feed to charge the aux battery at around 13.3V and cut out around 12.8V, meaning that the L322’s BMS will only charge the aux battery some of the time. The question is, is some of the time going to be enough for leisure battery usage, especially if running a fridge or other constant power draw gadgets? 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!

Yes i suspect you are right wrt to charging.
You probably need something with more intelligence such as the Victron products:
https://simplysplitcharge.co.uk/Shop-by-Br...arger.html

I think it is the normal working of the BMS.
I got a little anxious myself today, but as I dug into this, I'm now pretty confident, that it is normal.
My case:
A few days ago I changed my 4.5-year-old Bosch AGM for the exact same new one. Not that I had any problem with it, but to rule out a weak battery regarding the investigation of my FBH problem.

Changing the battery was an easy job and after resetting BMS with IID Tool, after the first start-up charging voltage Was reading 14.7V as I'm used to seeing.
So today I was doing other stuff with IID, while the car was idling and right away I noticed, that the charging voltage was only at 12.2V, which seemed alarming, although no error messages on the screen and I know they pop up on the screen when there were problems in the charging system since I've had a bad alternator on this car.
So immediately I looked at charging data with IID Tool and alternator current and load readings seemed to be where they should be and also reacted as expected when switching on and off different loads.
Next, I put a voltmeter on battery terminals to get an exact and reliable reading. It showed between 12.25-12.35V while idling.
So I went to my IID Tool archive and went through 2.5 years of data I have recorded. Almost always the charging voltage while idling has been between 13.5-14.7V, except for one time in hundreds of recordings it was reading 12.7V.

As I read through the workshop manual topic about the Charging system and BMS, I've come to the understanding, that probably the BMS is doing its discharging routine to determine the state of health of the new battery after the reset.
At least it seems logical.

With the old battery, the voltage was probably mostly over 14V because it wasn't so strong anymore.

What do you guys think?

Regards
Keijo

yeh agreed - mines been fine since i did the stater solenoid mod - but the charging goes up and down as posted.

I stopped worrying about low voltage/drain, with the relay MOD the car starts regardless of SOC and feels sold and reliable.

I do feel adding a secondary circuit is a better long term solution IMHO. SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

I have read the thread about the starter relay and cable, but can't relate. My 4.4 TDV8 does start in every condition with original set-up. It starts with weak battery and strong batter, with -35 degrees and +35 degrees outside. So I'm not considering this mod until some problem with it comes up. Maybe I would, if it shortened cranking time, does it? In my opinion this car is cranking a little longer than other makes.

Regards
Keijo

it will work until it wont anymore, then you have to replace the starter and consider the mod. Design is such it will arc and start then eventually fail due to poor contact/shoot. This leads to corroded contacts etc. A solid contact is always better in my mind and removes the weekness in the system. SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D