I would definitely replace the battery if it has been on there for a few years as it seems to be losing its charge and not recovering.
A healthy battery can lose its charge if the door light or radio has been on and flattened it but recover after a few minutes to then be able to start the engine.
If not, then you need to replace it with a good quality battery.....try Halfords for a replacement and think they will test for free but charge to replace it