There are already cheaper ones out there
I have used this non name brand on my S6e. Worked fine, did its job.
I am still debating if I want to go that road with my S7
http://www.amazon.com/Battery-Wuloo-Premium-External-Rechargeable/dp/B01CZM2Y2C/ref=pd_sim_sbs_107_3?ie=UTF8&dpID=41SpWW9heLL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=0PNR8EX7DMDC4CDK9C2Y