If you can get ahold of a 30C or 40C battery, your issues may go away. I had a similar issue with my Novak ESCs. The Novak paperwork and website specifically state that you need 25C or better to perform. The same may well be true of the Castle product.

I have not checked Castle's site as I don't own any of their stuff, but I have several friends who do use Castle products and my LHS sells Castle stuff. I've heard mostly good things about them.