Is the the original battery or a battery you got later that is after market?
If it the an after market one, then that could be your problem. While many things you can get after market work just fine, laptop batteries and charger cords are two things that often don't.
If it is the original battery, or an OEM one, then I would ask, is the battery actually working correctly or is it in need of replacement?
Lastly, was the laptop dropped at all, even from a small distance? If so, this can displace the battery and then you would need to open up the device to see about fixing this issue.
NOTE: If this laptop is under warranty still, please contact the manufacturer before doing any physical work on it.