Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 53)

3.
Charge the battery.
Slide the battery in (in the opposite direction from protective cover
removal) and make sure it is securely attached to the charger.
You can load a battery into either slot
or slot .
Charging begins, and the charge lamp blinks or lights up in green.
Charging is finished when all three charge lamps (50%/80%/100%)
are lit in green.
Charging takes approx. 2 hr. and 50 min. at room temperature (23°C/73°F) per
depleted battery.
The time required to charge the battery will vary greatly depending on
the ambient temperature and the battery's remaining capacity.
For safety reasons, charging in low temperatures (5–10°C/41–50°F) will take longer (up
to approx. 5 hr.).
Caution
Use Battery Charger LC-E19 to charge Battery Pack LP-E19 (both included). This
battery cannot be charged with Battery Charger LC-E4N/LC-E4.
Depending on the condition of the battery, charging to 100% capacity may not be
possible.
Note
If you load two batteries, they are charged one after another in the order you load
them.
Upon purchase, the battery is not fully charged.
Charge the battery before use.
53