my van won't start when the battery isn't fully charged, or drops to below 300 rpm. The local garage have tried everything to fix it. They are completely baffled. I need to drive it every day to keep battery charged but soon as any charge lost it stops starting. it's a new battery that's in the van. Auto electrics all checked. Everything seems to be fine. It runs great once it has started
Vital that you have correct battery with cranking amp , especially if it's a diesel. I would get the battery load tested ( even though it's new ) also alternator output .You could also check for any parasitic drain .