I do the same thing, deliberately have a phone that has user-swappable batteries. Why? I can insert a second battery that is fully charged instead of having to plug in the external battery (along with keeping track of the charging cable) and let it charge the internal battery. As a nice side bonus, I can also buy batteries which are larger than the stock battery. My Galaxy S4 GPE has aftermarket batteries available (mine is from Anker) that are essentially two stock batteries strapped together, or 5200mAh of capacity versus 2600mAh stock. Yes, the phone gets one "battery height" thicker but having two solid days of my normal use is outstanding.