It is quite possible that the battery is fine but does not show full charge.Or there may be other options.
Possible solutions
1. The battery must be discharged. It will be fine afterwards.
2. The battery may have been conditioned incorrectly. In that case one can try a few charge/discharge cycles and see if it recovers. If not, a new battery is indicated.
3. The charger may be faulty; does it charge other batteries correctly? Replace
4. The battery is faulty. replace
Batteries are a pain in the proverbial blunt end. I fail to see why cameras (and other appliances for that matter) cannot be designed more user-friendly. For instance it used to be that Metz flashes could take either: four AA cells, four rechargable AA cells, a rechargable Metz battery pack or a lithium battery. Now that was good design.