How old is the battery? What is it's history?
What charger are you using?
What is you knowledge level about NiMh charging?
Do you KNOW the battery is properly charged?
Charging NiMh can be a problem, especially if the battery is old or of questionable value.
Note - if you are trying to use consumer grade AAA or AA cells in a holder....forget it, won't work.
The battery+motor+prop provide the power so we need to know details about the whole package.