A low level of electrolyte fluid will cause the battery to discharge quickly.

Inspect the electrolyte level at least once a week. If it is low, remove the caps and add enough distilled water to bring the level between the upper and lower level (illustration).
Do not overfill.
Examine the specific gravity of the electrolyte with a hydrometer, especially during cold weather. If it is low, recharge the battery.
Battery Maintenance
Battery RechargingMazda 6 Owners Manual: Inside Trunk Release Lever (Some models)
Your vehicle is equipped with an inside trunk release lever that provides a means
of escape for children and adults in the event they become locked inside the trunk.
No matter how careful adults might be with keys and locking their cars, parents
should be aware that children may be tempted to p ...
Mazda 6 Owners Manual: No.1 air bag system warning light does not illuminate
Diagnostic Procedure
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while doing the inspection to discover whether
poor contact points are the cause of any intermittent malfunction. If there
is a problem, check to make sure connec ...