I just don't understand why if it is alternator why would it start first turn of the key 3 days later?. Thanks for your reply.

Because you probably completed the journey on battery power alone. The battery then had a few days to rest and probably recovered just enough to start the van.

OK thanks, so this would mean new alternator needed if it's below this? I just don't understand why if it is alternator why would it start first turn of the key 3 days later?. Thanks for your reply.

Could just be a slipping belt. Or, as already suggested, a wiring issue. For the latter case you could use your digital multimeter to do voltage drop testing, which can help you locate the fault.

Re your question, er dunno. TBH I dont find the rested battery explanation very convincing, especially given its a diesel, which tend to take a bit of cranking.

OTOH the battery having been discharged long term then jump started does suggest it might not be very healthy, probably wasn't fully charged, and it might have been asking a lot of the in-car charging system.

A poor/intermittent contact could produce your symptoms though, and voltage drop testing might help you find it, though I'd check battery terminals and earth connections are clean and tight first anyway.

It used to be that a diesel (with a mechanical fuel pump) would run indefinitely while electrically stone dead but that probably isn't the case any more.

Edited by edlithgow on 03/01/2024 at 13:53