Nikon D6 Reference Manual page 46

A WARNING (Batteries)
Keep batteries out of reach of children.
Should a child swallow a battery, seek immediate medical attention.
Keep batteries out of reach of household pets and other animals.
The batteries could leak, overheat, rupture, or catch fire if bitten,
chewed, or otherwise damaged by animals.
Do not immerse batteries in water or expose to rain.
Failure to observe this precaution could result in fire or product
malfunction. Immediately dry the product with a towel or similar object
should it become wet.
Discontinue use immediately should you notice any changes in the
batteries, such as discoloration or deformation. Cease charging
EN-EL18c rechargeable batteries if they do not charge in the
specified period of time.
Failure to observe these precautions could result in the batteries leaking,
overheating, rupturing, or catching fire.
When batteries are no longer needed, insulate the terminals with
tape.
Overheating, rupture, or fire may result should metal objects come into
contact with the terminals.
If battery liquid comes into contact with a person's skin or clothing,
immediately rinse the affected area with plenty of clean water.
Failure to observe this precaution could result in skin irritation.
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For Your Safety