Mio DigiWalker A501 User Manual page 24

If you need to remove the battery, use your finger to push on the finger
grip and lift the battery out of the compartment. DO NOT use
screwdrivers or metallic tool edges to extract the battery from the device
as they may damage and irreversibly alter the battery's behavior.
4. Replace the back cover: direct the back cover to the locking latches on
the device and close the back cover. Then press the mid section on each
side of the back cover to lock it into place.
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Getting Started