Canon Powershot A590 IS User Manual page 177

The CB-5AH/CB-5AHE battery charger can only be used to
charge Canon AA-size NiMH batteries NB-3AH.
Do not mix batteries with different purchase dates or
different charge states. When recharging batteries, always
recharge both of them at the same time.
Do not attempt to recharge fully charged batteries, as doing
so may reduce or impair battery performance. Also, do not
charge batteries for more than 24 consecutive hours.
Do not recharge batteries in enclosed areas that tend to
retain heat.
Do not recharge the batteries until the LCD monitor displays
the "Change the batteries" message. Repeatedly recharging
batteries before they become depleted may cause batteries
to lose capacity.
Wipe the battery terminals well with a dry cloth in the
following situations, as the terminals may be soiled with oil
from one's skin or other dirt:
- If the battery usage time has considerably diminished
- If the number of recordable images has considerably
diminished
- When charging the batteries (insert and remove the
batteries two or three times before charging)
- When charging completes in a space of a few minutes (the
battery charger indicator remains lit)
You may not be able to fully charge the batteries due to their
specifications right after purchase or after long periods of
nonuse. If this happens, after fully charging them, use the
batteries until their charge is depleted. After doing this
several times, battery performance will be restored.
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