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Battery Not Supported Message
If the device displays the message "Battery Not Supported" or "Unsupported Battery Type" when powering on the device, it may indicate that the Garmin software is out of date, the battery charge level is very low or that battery is not a Garmin branded battery.
To update your device, download and install Garmin Express to the computer. For more information on updating device software see Installing the Latest Software Updates to Your Outdoor Handheld.
Also make sure to try charging Garmin device overnight ensure it was just not a battery with a very low charge.
If the battery is not a Garmin branded battery, a new battery can be purchased here: Garmin Lithium-ion Battery Pack.