Sony MZ-B3 Operating Instructions Manual page 18

Charging the built-in battery
for the clock
After setting the clock, leave the
recorder with the dry batteries
installed for about 2 hours to charge
the built-in battery for the clock.
You can use the recorder while
charging. Once charged, the built-in
battery should last about a month
without connecting to any of the
power sources. The recorder will
automatically charge the built-in
battery while connected to dry
batteries, AC power, or a rechargeable
battery.
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SONY MZ-B3 (E) 3-798-610-22(1)