Mazda 6 Owner's Manual page 605

Maintenance and Care
Owner Maintenance
WARNING
Keep all ames, including cigarettes, and sparks away from open battery cells:
Flames and sparks near open battery cells are dangerous. Hydrogen gas, produced
during normal battery operation, could ignite and cause the battery to explode. An
exploding battery can cause serious burns and injuries.
NOTE
Before performing battery maintenance, remove the battery cover.
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