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7 Batteries
When a charged battery is in the computer and the computer is not plugged into external power, the computer runs on battery power. When the computer is plugged into external AC power, the computer runs on AC power.
If the computer contains a charged battery and is running on external AC power supplied through the AC adapter, the computer switches to battery power if the AC adapter is disconnected from the computer.
NOTE The display brightness is automatically decreased to save battery life when you disconnect AC power.
You can keep a battery in the computer or remove and store it, depending on how you work. Keeping the battery in the computer whenever the computer is plugged into external AC power charges the battery and protects your work in case of a power outage. However, a battery in the computer slowly discharges when the computer is turned off and not plugged into external power.
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