What's the benefit of an extra cell phone battery vs. external battery cases?

Episode 962 (19:05)

Colin from Huntington Beach, CA
Mophie Juice Pack

Colin says one way Leo can save money on cell phone batteries is to buy an external battery. Leo says that he has plenty of external battery cases, but he still has to carry them around. He prefers the extra battery because it fits in his pocket. Leo does like the Mophie Juice Pack Air case, which puts the battery inside the case. He also says that Samsung has killed the myth that Apple doesn't let the battery be removable for the reason of keeping the phone slim. He thinks it's because Apple just doesn't want people inside the phone.