Oh and the laptop is nearly 6 years old so I guess its done well
Batteries don't last forever. There is some deb ate as to whether a battery should be left in the laptop whilst on mains supply unless during a charge cycle.
Well EC tbh I don't know and have never really given it much thought. I am told my laptop doesn't need a battery unless, obviously, I intend to use it away from the mains supply, which I don't. Would that be correct?
Yes, if you are using it away from the main supply then a battery is required.