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: Refrigerant pressure switch inspection
1. Install the SST (gas charging set).
2. Disconnect the refrigerant pressure switch connector.
3. Verify the high-pressure side reading of the SST (manifold gauge)
and continuity between the terminals of the refrigerant pressure switch.
If not as specified, replace the refrigerant pressure ...
Mazda 6 Owners Manual: Pid/data monitor inspection
1. Connect the WDS or equivalent to the DLC-2.
2. Measure the PID value.
Note
Perform part inspection for the output device after PCM
inspection.
The PID/DATA MONITOR function monitors the calculated value of the
input/output signals in the PCM. Therefore, if a monitored value ...