I have used one of these and was very happy with it. I would also highly suggest yo7 ditch the nicad pack and go with a 3 cell Lipo. 850 mah would work just fine for up to 3 climb outs per charge.

https://alofthobbies.com/dualsky-xm2838eg-9l.html

https://www.buddyrc.com/tattu-850mah...xt30-plug.html