Apparently the battery is Circuit Board mounted and is a backup memory battery.
Li (lithium) battery • T
he Li battery is mounted on the printed circuit board in the data processing unit "QM-Data". Do not dispose of the data processing unit by burning it. If the data processing unit is thrown into fire, the battery may leak chemicals, burst, or burn violently. Comply with government regulations regarding the disposal method.
and
• This error message indicates that the memory backup battery is low, and that if you continue to use the data processing unit "QM-Data", backup will not be performed. Save the part programs and measured data stored in the internal memory of the data processing unit to the floppy disk or to a personal computer. •
Contact your supplier to replace the battery.
It also says changing the battery removes any saved data.
So if you are looking to do it yourself, look for screws to get inside.
https://www.mitutoyo.com/webfoo/wp-content/uploads/QM-DATA200_2222.pdf
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