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: After repair procedure
Caution
After repairing a malfunction, perform this procedure to verify that the
malfunction has been corrected.
When this procedure is carried out, be sure to drive the vehicle at lawful
speed and pay attention to the other vehicles.
1. Connect the WDS or equivalent to the DLC-2.
2. Turn th ...
Mazda 6 Owners Manual: Key Battery Replacement
If the buttons on the transmitter are inoperable and the operation indicator
light does not flash, the battery may be dead.
Replace with a new battery before the transmitter becomes unusable.
CAUTION
Make sure the battery is installed correctly. Battery leakage could occur
if it is not in ...