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: Active Adaptive Shift (AAS)
Active Adaptive Shift (AAS) automatically controls the transaxle shift points
to best suit the road conditions and driver input. This improves driving feel. The
transaxle may switch to AAS mode when driving up and down slopes, cornering, driving
at high elevations, or depressing the accelerato ...
Mazda 6 Owners Manual: Cruise Control (Some models)
With cruise control, you can set and automatically maintain any speed of more
than about 25 km/h (16 mph).
WARNING
Do not use the cruise control under the following conditions: Using
the cruise control under the following conditions is dangerous and could result
in loss of vehicle control.
...