Hi friends as I titled buy a genuine powerbank because in market there are so many fake powerbanks available sometimes you cant recognize it so always buy from trusted online sites where they give 1 year warranty . Now you need to decide powerbank mah according to your need I think the 10000-13000 mah is the best one and yes guys please buy the powerbank which comes with original samsung cells because u dont need to worry if the cells are from samsung we all know the samsung brand and its quality there are so many designs of powerbank are available in market keep in your mind is that you have to charge powerbank for nearly 10-12 hours if your buying a 13000 mah powerbank and it will charges your mobile morethan 3 times if your phone having 3000mah battery this time the powerbank brand name is very popular is Ambrane u can buy the powerbank from ambrane and u will love the perfomance of brane series of powerbanks because I am using it for last 1 year and it works very well u hav many choice it depend upto you guys many brands are available online too so guys go for it .