I also used to run one like that, i only had one nun chuck, so i carryed around a Ump mag pouch i had. Honestly i think they make them specificly for batterys now, but. i got some like foot long velcrow strips and i would strap them around the crane to attach the pouch to the crane stock. I could get it to fit snug into the space under the crane pressed against the slig adaptor parts on the back lower part of the crane, around where the retractable adjustment lever is.
it worked fine for me and really never got in the way..