Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 45)

45
Charging the Battery
This is a recommendation that you calibrate (discharge) the battery
so that the camera can accurately determine its capacity and display
its battery level accurately.
It is recommended that you perform calibration if the < CAL > lamp
blinks in green. If you want to just recharge the battery, you can let
the battery start recharging automatically after approx. 10 sec.
If you want to do the calibration, press the < CALIBRATE > button
while the < CAL > lamp is blinking in green. When the < CAL > lamp
lights up in green, the battery will start to discharge.
After the battery is finished discharging, the battery will start
recharging automatically. Note that the less depleted the battery, the
longer the discharging will take. The <
14h >, < 4h >, and < 2h > figures
respectively indicate the approximate number of hours it will take to
complete the power discharge. If the <
14h > indicator blinks in green,
it will take approx. 4 up to approx. 16 hours to complete the
discharge.
The calibration (power discharge) will completely drain the battery’s
power. Therefore, it will take approx. 2 hr. 50 min. to fully charge the
LP-E19. If you want to stop the calibration before it is completed and
start recharging the battery, remove the battery from the charger and
attach it again.
The <CAL> lamp blinks
If the battery is recharged and used repeatedly without calibration, the
battery level (p.54) may not be displayed accurately.
Although one battery can be recharged and another calibrated at the
same time, two batteries cannot be recharged or calibrated at the same
time.
For battery calibration, performing with a battery nearly exhausted is
recommended. When calibrating a fully-charged Battery Pack LP-E19, it
will take approx. 18 hr. 50 min. before calibration is complete and the
battery is recharged. With the same charge status, it will take approx. 15
hr. 20 min. with the LP-E4N, and approx. 14 hr. 20 min. with the LP-E4.