I have heard local bad stories about the use of NiMH batteries and them not being able to handle the load of multiple servos and losing a plane. I will be getting a 6v NiCd for my extra since I am using standard servos. I know that NiCd actually offer more punch, that's why they were more popular with electric race cars than the new NiMH. NiMH is a little more user friendly because they don't have memory issues.