It's just a battery extender used to charge up your iPhone's battery when its battery needs charging. So keep it off until needed. Because if you turn it on right away then your iPhone's battery will be in a constant state of charge and thus shorten its battery life.
It doesn't replace the iPhone's battery, it's a battery charger case. So only use it when you need to recharge the iPhone's battery. I thought everyone knew this?
Oh, I wasn't aware the original Mophie was designed to be used that way.there other battery cases out there like the original Mophie where it's meant to be on as soon as the iPhone is on until it uses the battery up; then after it drains it uses the iPhones battery.