My battery is not charging for some time?

when the adapter is plugged in it shows not charging but after some time it shows charging and again same process it will charge for some time and not charging for some time.is this due to overheat of laptop? or the battery is damaged?or the adapter is damaged? but overall it will charge fully and after i unplug the adapter the charge will decrease very rapid.the battery and adapter are 3 years old. do i need to change them ?