Canon EOS 350D Instruction Manual page 21

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Do not use the battery charger to recharge any battery other than
Battery Pack NB-2LH.
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To prevent the battery performance from degrading, avoid recharging the
battery pack for 24 consecutive hours or longer.
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If the battery is left in the camera for a prolonged period without the
camera being used, a low electrical current may be discharged
excessively and the battery's service life may be affected. When not
using the camera, remove the battery and attach the protective cover to
prevent shorting. Before using the camera again, be sure to recharge the
battery.
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You can attach the protective cover to the battery
and set the direction of the cover marking to
indicate whether the battery has been recharged
or not.
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After recharging the battery, detach it and unplug
the power cord from the power outlet.
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The time required to recharge the battery depends on the ambient
temperature and the battery's recharge level.
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The battery pack can operate in temperatures from 0°C to 40°C (32°F to
104°F). However, for full operating performance, using it between 10°C
(50°F) and 30°C (86°F) is recommended. In cold locations such as ski
areas, battery performance temporarily decreases and the effective time
may be shorter.
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If effective time is sharply reduced even after normal recharging, the
battery pack may have reached its service life. Replace it with a new
battery.
Recharging the Battery
21