Like someone mentioned, look for a buddy code. I checked out one earlier that took the 2200 3S nanotech that I use down to 11 bucks. I'll try to find it again.
Just keep saving up and buy 2200mah 3s 11.1v all the time then they no longer become back up batteries but just batteries.....seriously though if you are flying the same type of plane as most hobbyists then these batteries are spot on and as you branch out into tris and quads and other machines that size powerpack is good for all......keep flying
Good point. 2200's are very versatile. I use them in my Blade 400 helicopter, my Supercub, they can be used in quad copters, lots of 480 size 3D and sport planes etc. Of course if 1500 is what you want go for it. Just agreeing with Brian Fred Carr.
Lots of answers you got there.
I would go for the 850 as you suggested - 2 or 3 in parallel if you need long time and just one if you want the lightest setup for thermalling. The 850 (high C) will be perfect for smaller foamies like FUNBAT and wings.
The nano-tech batteries hold a higher charge for much longer. That doesn't mean longer flight times, but your battery voltage will hold at higher voltages allowing for more power to your motor. I've got the buddy codes for some of the 3S Nano-techs you were talking about here: