Good day!

Well, lower temps are great for electronics, but not so much for items that need heat to run... Batteries always have a CCA (Cold Cranking Amps) and that is generally what everyone goes by... It will say normal cranking amps around there somewhere and will be a bit higher... The battery might be taxed a bit more in the cold due to the longer wait time needed to get the glow plugs up to temp before starting... Diesels are always harder to start due to their compression in the cylinders... Everything does point to the battery, but I wouldn't rule out the starter entirely... I don't think the fuel pump relay or pump would have issues just in the cold... I've actually seen fuel pumps stop working after heating up, then working again once cooled off... Again, not impossible I guess... I would swap in a known good battery (from a different vehicle you have??), just to see what happens... If you are still having the same issues, I would do the starter... Just my two cents...

Good luck and let us know what you discover!

Cheers!!

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2001 E53 X5 4.4i (03-07-2001 build date) White exterior / hellbeige interior (6MT swap vehicle - Manny)
2002 E53 X5 4.6is (12-20-2001 build date) Imola Red exterior / M-texture interior (Red)
2003 E53 X5 4.4i (06-26-2003 build date) Silver exterior / Black interior (Silvester II)
2008 Mini Cooper S ragtop (04-17-2008 build date) Dark Silver exterior / Gray interior ( Topless)
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