Greetings from a less cold Sweden!
Here are some humble suggestions and questions from a nordic beginner that has not (yet) flown....:-)

What about those plastic frames where you insert AA-batteries??
They could be got in several configurations,2,4,6 & 8, etc...and are quite light too. I got one as batterypack for my Hitec Flash 5X,since I have found a Tjeck dude that sell AA-NiMh batteries that contain 2950 Mha and AAA-batteries with 1450 Mha on the Net. For the reciver I also found an english site that sell batterypacks and bought one 2200 Mha-6volt.However, isn´t the objective to have as much electricity available as you possible can??
If using frames,the eventual danger with soldering is moot and the charging could also be done in an ordinary charger as well as a field one, and if for some reason one battery turns bad, one can replace the one and not the whole pack.
Sincerely yours,
Mikke