Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 46)

Charging the Battery
46
If the charging starts and only the lamp with the < 100% > mark lights
up in green right away, it means the battery’s internal temperature is
outside the required temperature range. The battery will start
recharging automatically when the internal temperature is within the
range of 5°C - 40°C / 41°F - 104°F.
When two batteries are attached to the charger and only the lamp
with the <
100% > mark on the second battery side lights up in green,
it indicates that it is in a waiting status.
The charger cannot charge batteries other than the provided LP-E19
and LP-E4N/LP-E4. The three charge lamps and <
CAL > lamp will
blink in green.
While charging a battery, if the three charge lamps blink in green
consecutively or if they blink consecutively in green with the <
CAL >
lamp blinking in green, remove the battery from the charger. Contact
your dealer or the nearest Canon Service Center.
If the three charge lamps blink during calibration, remove the battery
from the charger. Contact your dealer or the nearest Canon Service
Center.
Right after attaching the battery, only the lamp with
the <100%> mark lights up
All three charge lamps blink