Canon Powershot A590 IS User Manual page 178

176
If you store batteries for a long period of time (about 1 year),
it is recommended that you deplete the batteries in the
camera and to then store them at room temperature (0 to
30°C/32 to 90°F) in low humidity. Storing them in a fully
charged condition can shorten their lifespan or degrade their
performance.
Again, if you do not use batteries for more than 1 year, fully
charge them once a year and deplete them in the camera
before storing them.
If the battery usage time has become considerably low
despite wiping the terminals and charging them until the
battery charger indicator remains lit, this may indicate that
the batteries have reached the end of their lifespan. Replace
them with new batteries. If you are purchasing new
batteries, look for Canon AA-size NiMH batteries.
Leaving batteries in the camera or charger may result in
damage from battery leakage. When not in use, remove the
batteries from the camera or charger and store them in a
cool, dry location.
It takes approximately 4 hours 40 minutes for the charger to
fully recharge the batteries after they have been depleted.
When two batteries are placed on each side of the charger,
recharging will take approximately two hours (as determined
by testing at Canon facilities).
Charge batteries in an environment where the temperature is
in the range of 0 to 35°C (32 to 95°F).
The charging time varies according to the ambient
temperature and to the battery charge state.
The battery charger may emit noise while charging. This is
not a malfunction.