Solar Cell and Rechargeable battery technology is becoming very popular in the Casio line of watches. Following is an example of how long the watch needs to fully charge under different lighting conditions. If the watch is Outdoors (on a sunny day) and displays LOW, or there is nothing marked, it will take 1 hour to have MID displayed, and 14 more hours to have High displayed. 3 additional hours, and the watch will be fully charged.



Battery Power Indicator

Outdoor sunlight

Sunlight thru Window

Cloudy Day thru Window

Indoor Fluorescent*

Level 1


3 hrs

14 hrs

28 hrs


Level 2


14 hrs

70 hrs

143 hrs


Level 3


1 hr

3 hrs

5 hrs

57 hrs

Level 4

Nothing on the display, watch battery has completely discharged

Note that the times are cumulative, so if the watch is completely dead, it would take 1+14+3 hours of direct Outdoor sunlight to fully charge.  If through a window, 84 hours.  This means that with a window that gets 8 hours of sunlight a day a full charge could take 10 days.  However, once charged only 5 minutes of direct outdoor sunlight a day is needed to maintain the charge.  See below for more information.

Actual exposure times may vary due to cloud cover, and the amount of the Solar Cell that "sees" the light. For instance, if a shirtsleeve is covering part of the Solar Cell, the watch may take longer to charge.

From a HIGH, or Full Charge, the various watches will last for 5-9 months (depending on the model) under the following conditions:

  • Watch is not exposed to light (not recharging)
  • Display on 18 hours a day, Sleep state 6 hours per day
  • 1 backlight operation per day
  • 10 seconds of alarm operation per day
  • 1 use of Specialty Function (4 time calibrations, 1 countdown, Compass use, etc. depending on the model)

Use of the backlight, alarms, and timers more often will cause the battery to be depleted more rapidly. Exposing the watch to light for the periods shown below each day restores the power used by the above operating conditions.

Exposure Level

Approximate Exposure Time

Outdoor Sunlight

5 minutes

Sunlight thru Window

24 minutes

Cloudy Day thru Window

48 minutes

Indoor Fluorescent

8 hours


If the watch is not recharged each day, the battery will slowly deplete, and it can take days to recharge (see the table at the top of this page). Charging daily or weekly will extend the battery life, and the life of the watch. If a Customer is complaining that the watch will not accept a charge, have them put the watch in a sunny window for a few days (even in a sunny window a full charge can take 87 hours and most windows only get 8-10 hours of direct sun per day) and see if the watch starts working.

*Indoor Fluorescent light takes an extremely long time to charge the battery. Many customers that may be experiencing frequent LOW battery warnings may only be charging the watch for a few hours in the MID range, and think the watch is charged. The "-----------" means that the watch will take a tremendously long time to charge under these conditions.



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