Casio 3476 Owner's Manual page 59

Battery: One lithium battery (Type: CR1620)
Approximately 3 years on type CR1620 (assuming alarm operation 10 seconds
per day, one illumination operation 3 seconds per day and one signal reception
6 minutes per day)
Frequent use of illumination can shorten battery operating time.
Specifications are subject to change without notice.
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