When the iPhone is connected to the MiLi PowerSpring 4 Extended Battery, the MiLi’s internal smart chip efficiently prioritizes power consumption. If the MiLi is being charged, the iPhone’s consumption comes first from the USB power source. When the MiLi is not being charged, the iPhone’s power consumption comes from the MiLi battery. The iPhone will continue to use the battery until the MiLi’s remaining charge is less than 5 percent.