SUUNTO M1 - Manual (Page 28)

NOTE: Carefully ensure that the plastic O ring is properly placed so that the
wristop computer remains water-resistant. Careless battery replacement may void
the warranty.
NOTE: Be careful with the spring in the battery compartment (see illustration).
If the spring is damaged, please send your device to an authorized Suunto
representative for service.
NOTE: When replacing the battery, only the time and date change. Previous
initial settings and recorded exercises are restored.
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