I know this is an old thread, but it's literally exactly what I'm trying to accomplish now. I've been through the 100+ page Battery Mod Info thread, and all this thread, and was wondering if interest in this just died, or did someone find anything better than a $500 battery from overseas?
And just a side note: Does anyone have a copy of the Dropbox - Battery Mod DJI inspire.pdf as it's a dead link nowadays.
Thanks for all the work everyone has posted on this.