Citizen E610 Instruction Manual page 68

Charging time for 1 day of operation: Time required for charging the watch to run
normally for 1 day
[Note]
Once fully charged, the watch has a continuous operating time of about six months
without further charging. When the Power Save function has been activated, the watch
will continue to keep the correct time for about one year. However, if the watch stops
running as a result of being insufficiently charged, a considerable amount of time is
required to charge so that it starts running again as is indicated in the table. It is
therefore recommended to charge the watch at least once a month by exposing to direct
sunlight.
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