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: Closing the Hood
1. Check under the hood area to make certain all filler caps are in place and
all loose items (e.g. tools, oil containers, etc.) have been removed.
2. Lift the hood, grasp the padded area on the support rod, and secure the support
rod in the clip. Verify that the support rod is secured in the c ...
Mazda 6 Owners Manual: Meters and Gauges
Instrument Cluster Type A
Type B
Steering Switch
1 - Speedometer 2 - Odometer, Trip Meter and Trip Meter Selector 3 - Tachometer
4 - Dashboard Illumination 5 - Trip Computer and INFO Switch 6 - Engine Coolant
Temperature Gauge 7 - Fuel Gauge 8 - Outside Temperature Display 9 - Cruise
...