I thought the same myself that it might be immobiliser at fault but then once it has a fresh battery it starts and runs fine multiple times it’s only after left for 5 mins or so with key out and door shut that it then won’t start again

Hi looking for some advice or if anyone has had the same problems. A few weeks ago the battery died in my disco so first thing I did was attempted to jumpstart it to which it refused to even crank over even when tried with multiple vehicles. So took the battery off the truck and charged battery...