Going to the US next week and will be keeping in touch with business here very frequently. Just bought my first i phone 5s and getting thoroughly confused which external battery to go for. I see the Anker 2400 on amazon but problem with flimsy part on it and thought that might be the one. Is this better than the Mophie Juice Pack plus pls? I have an otterbox defender series cover which I guess I will have to take off for any of these external batteries. Any suggestions gratefully received!