My GWS Pico Stik climbs like a homesick angel.
I even have our new float kit on it. The extra weight and drag are not even noticeable.
See the video of it flying in –28 degree weather with NiMh cells. (I keep them in my pocket so they stay warm)

http://www.climateboatworks.com/video/videopage.htm

There must be something not right. How are you charging your batteries?
A lot of people blame the plane when it is the battery pack that is actually the problem. A cheap charger is just that. If you are going to fly electrics, get yourself a good digital charger. It makes all the difference in the world.