While hot swapping the battery, notice the following behaviors:
The tablet display gets dimmer. When the charged battery is in the tablet, the display brightens again.
The battery status LED turns blue when the system is on and no main battery is present. When you put a charged battery in the tablet, the LED lights turn green again.
The power button is disabled. (The power button is disabled at any time the tablet has no battery and is not running on AC power through the power adapter.)