If you use a vehicle everyday and it has a flat battery one morning, chances are the battery is dead. If you haven't used a vehicle for five months then chances are it just needs charging.
A case in point is my tractor. Dead as a door nail. Half a day on charge and it coughs into life with a cloud of black smoke (or not on Sunday - needs a bit longer on charge).
This little battery charger has had some use over the last few years. I think as soon as you have a smallholding you have to have something that doesn't start first time, kind of an unwritten rule.
Growing up on the farm was no different. I remember that we used to have to leave certain vehicles within range of an electric socket or next to another, more reliable, vehicle so it could be jump started in the morning, sorting this minor problem was something we learnt at a fairly young age.
So what's the most unreliable (but easy to sort) vehicle you've owned or currently own?