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: Clutch disc inspection
1. Using vernier calipers, measure the thickness of the lining at a rivet
head on both sides.
Replace the clutch disc if its thickness is less than the minimum.
Thickness
0.3 mm {0.012 in} min.
2. Measure the clutch disc runout using a dial indicator.
If the runout is excessiv ...
Mazda 6 Owners Manual: Ignition switch inspection
1. Disconnect the negative battery cable.
2. Remove the column cover. (See COLUMN COVER REMOVAL/INSTALLATION)
3. Disconnect the ignition switch connectors.
4. Inspect for continuity between the ignition switch terminals using an
ohmmeter.
If not as specified, replace the ignition switch.
...