Parts of the transmitter are regulated and parts are not. Also, the transmitter is certified with the NiCd pack. We'd not know the affect if a higher-voltage battery pack were used. It wasn't certified with drycells.

We'd have to suggest that you make up a 1100mAH NiCd pack. You can get such packs that are virtually the same physical size as the standard 600mAH pack. NiMh packs would also work because they are of a similar size to NiCd packs.

Since a properly-regulated and properly-protected Li-poly or Li-Ion battery pack is not availble for the 9C yet, we'd be quite reluctant to install one, especially a home-made one.