The chargers supplied with the Parkzone and Hobbyzone airplanes are a cheap version of a peak charger . Sometimes they false peak , and need to be unplugged and started again to reach full charge . You may have to do this a couple times to get the battery fully charged . You can try cycling the batteries as suggested above , it does work . You can use the 9.6 volt battery , just be sure to not run the plane at full throttle for extended periods of time . I used to run the 10.8 volt Mustang batteries in my old Aerobird and it made quite a bit of difference in the power . I burned out one speed controller though running it at full throttle for too long . The extra power made that plane way more fun to fly .