When an app starts up, it uses the CPU intensively for a second or so. Some apps need more. That is the cost of closing/reopening. The CPU uses real power when

When an app starts up, it uses the CPU intensively for a second or so. Some apps need more. That is the cost of closing/reopening. The CPU uses real power when it runs at full speed. The cost scales with the number of reopenings, though, which may be very low. BTW, looking at the Android history makes me doubt that advances in battery will lead to background apps. Lead to lighter devices, yes, longer battery lifetime, yes, but background apps?