The plastic battery straps are ideal imo. They spread the load across the entire pack instead of just the edges of the pack, like pulley straps do. I would buy them if the length was about 25mm longer, plus you get two for $40, not one. Sure they are injection molded, but lighter is better as long as they don't break.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy