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: Technical data
ENGINE
LUBRICATION SYSTEM
Note
The maintenance intervals on scheduled maintenance table (See
SCHEDULED MAINTENANCE TABLE) can only be supported by the use of following
oils.
Recommended engine oil
COOLING SYSTEM
FUEL AND EMISSION CONTROL SYSTEMS
ENGINE ELECTRICAL SYSTEM
...
Mazda 6 Owners Manual: Shroud panel removal/installation
1. Remove the bonnet. (See BONNET REMOVAL/INSTALLATION.)
2. Remove the front bumper. (See FRONT BUMPER REMOVAL/INSTALLATION.)
3. Remove the front combination light. (See FRONT COMBINATION LIGHT
REMOVAL/INSTALLATION.)
4. Remove the front bumper reinforcement. (See BUMPER REINFORCEMENT
REMOVAL/ ...