Canon EOS 1D Mark II N Instruction Manual page 23

Refreshing the Battery
If the Ni-MH battery is repeatedly recharged before it has discharged
completely, the capacity degrades due to the memory effect. To
eliminate this memory effect, follow the procedure below.
Connect the battery.
1
Hold down the button until the orange <REFRESH>
2
lamp lights.
The battery will begin to discharge.
The discharge time will vary depending on the remaining capacity.
Discharging a fully-charged battery will take about 8.5 hours.
When the discharge is completed, charging will start
automatically.
To interrupt the discharge, press the <REFRESH> button until the
red <CHARGE> lamp lights.
When two batteries are connected, the battery which was connected first
will be charged first. After the first battery is fully charged, the other
battery will start charging automatically. The battery waiting to be
charged will have the <CHARGE> lamp blinking slowly (every other
second). And when two batteries are to be discharged, the battery
waiting to be discharged will have the <REFRESH> lamp blinking slowly.
Also, with two batteries connected, one can be charging while the other
is discharging.
If you only want to discharge the battery, you need not connect the power
cord to a power outlet. Press the <REFRESH> button. When the
discharge is completed, the <REFRESH> lamp will turn off.
The NC-E2 is compatible with 100-240 V AC. It can also be used with a
commercially-available AC plug compatible with the respective country's
power outlet.
Whenever the battery is out of the camera, be sure to attach the
protective cover to prevent a short circuit.
The Ni-MH battery discharges naturally even while it is not used. You
should charge the battery at least once every 6 months.
The NP-E3 is dedicated to the EOS-1D series camera. It cannot be used
with Power Drive Booster PB-E2.
Recharging the Battery
23