Hello Gents, new member here first post and desperate, Please help!!

Never had an issue with the car until about 10 weeks ago my L322 2012 TDV8 that I only drive at weekends as I work away wouldn't start. I jump started it and it was fine for the rest of the weekend. The next weekend the same thing happened I assumed it was a cold weather and aging battery probable, that I would get round to replacing when I had some free time/spare money.

That went on for 4 weekends, then the 5th weekend it wouldn't start and it wouldn't jump start. I gave in and took a working battery out of a van (same size), still wouldn't start just the solenoid click but no crank.

I did some reading and figured it sounded logical that the low voltage and jump starting ect may have damaged the starter moter so after checking it was receiving voltage (which it was) I spent a day replacing that same symptom just the click.

So more reading and I disconnected the start moter cable and connected a second battery directly to the start moter positive and earthed it to the chassis it started, I figured as the alternator is connected to that cable and I was suffering low voltage so maybe that's the issue, I changed the alternator for a new one (much bigger job than I anticipated). Once I got everything back together, the same symptom just the click.

I then changed the 400amp mega fuse just as I had done everything else I could think of, still just a click.

I tried again and the car starts with the battery directly to the starter moter technique so,

The the new start moter is engaging the fly wheel teeth and turns when connected to a separate power supply,

the engine is turning over and running, the cooling fan is spinning and there's no leaks ( I've refilled the coolant)

The new alternator is upping the voltage when the engine is running so that's working.

The voltage at the starter moter cable is the same as the battery so the mega fuse is good.

I have a small cheap obd2 reader that says no codes.

I have done everything I can think of what am I missing?

Potentially a couple of things being a 4.4 TDV8 I can think of.

1. Failed terminals/cables. One or several may need replacing - the parts were cheap from the factory and have been known to fail - either from the alternator or starter motor.

2. Faulty alternator. The diode set is known to go AWOL and drain all battery, eventually leading to starting problems

I see you've changed the starter motor, so highly unlikely to be that. 2015 Range Rover Autobiography 4.4 SDV8

Electrics is not my ‘forte’……but……I thought I read somewhere that the earth strap from the battery to the chassis is in more than one piece, two possibly three? Whether that’s relevant I don’t know, just trying to help😜.
Good mobile car sparky is the last resort? 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
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https://www.fullfatrr.com/forum/topic50836.html

Well known issue. 2011 Vogue SE 4.4 TDV8