JR says its not recommended due the extra voltage on the output transitor. I know some are using them but the official word is not recommended.
They do however now sell a 2500mah nimh that I am using in my 10X. I replaced the battery in the 10X cartridge with this new pack. Its working great.
http://www.horizonhobby.com/Products...rodID=JRPB5011
Troy Newman
Team JR