BTW i don't understand the concept of removing the battery.
A boot in this context is defined as any activity of the device (flashing LED, some display on screen) that doesn't result in and stop at the NOKIA boot screen with USB icon. Especially "charging" actually also implies a boot of the system, and there's no lower limit for duration of such an accidental boot, 5s are more than enough to ruin your freshly flashed system.