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: Dtc c1095, c1096
Caution
When attaching the tester lead to the ABS (ABS/TCS) HU/CM harnesses
connector the SST (49 G066 001) must be used. (See ABS (ABS/TCS) HU/CM
INSPECTION.)
Diagnostic procedure
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Mazda 6 Owners Manual: No.2 air bag system warning light is illuminated all the time
Diagnostic Procedure
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while doing the inspection to discover whether
poor contact points are the cause of any intermittent malfunction. If there
is a problem, check to make sure connec ...