300Tdi trouble starting after running

Hi,
I have a 1995 300Tdi Disco. I am having a few problems getting it started after it has been running for a while.

I.e if i go to the petrol station and fill up, i am not moving from the forecourt for about 10 minutes. Its seems like the battery is flat when i turn the key. If i leave it for about 10 minutes it fires up first time.
I recently left it for 5 weeks and it fired up first turn of the key.

The multimeter says it is charging at about 14.5V when the engine is running.

Alternator voltage rounds right.

does it turn over at all when it dosent start? dosent sound sluggesh or no nasty noises (starter teeth skipping etc)? vast amounts of smoke out the exhaust when cranking?

No funny noises or excessive smoke. It turns over really sluggishly.

so it turns over sluggishly but then 10mins later it turns over fine and starts easy? strange one

Have you tried another battery? Could be that your alternator is is a1 condition so you get a good charging voltage but ur battery is on the way out.

also make sure your earth straps are all sound. try taking another strap from the engine block to the battery negative next time it wont start then try.

Battery sounds like it's draining and / or not holding a charge. Time for a replacement battery and earth Isolation switch