Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 504)

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If a problem occurs with the camera, first consult this Troubleshooting
Guide. If this Troubleshooting Guide does not resolve the problem,
contact your dealer or nearest Canon Service Center.
Provided Battery Charger LC-E19 can only charge the provided
Battery Pack LP-E19 and genuine Battery Pack LP-E4N/LP-E4.
Battery Charger LC-E4N/LC-E4 cannot charge the provided Battery
Pack LP-E19.
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. For details, see page 45.
If the charging starts and only the < 100% > lamp lights in green right
away, it means the battery’s internal temperature is outside the
appropriate temperature range. The battery will start recharging
automatically when the internal temperature is within 5°C - 40°C / 41°F
- 104°F.
Troubleshooting Guide
Power-Related Problems
The battery does not recharge.
The charger’s lamp blinks.
Right after attaching the battery to the charger, only
the <100%> lamp lights up.