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: Transmitter battery inspection
Caution
Since the battery voltage does not drop fully if the button is
pushed for only 4 seconds or less, it can not be properly examined to see
whether it is good or bad. Always push the button for 5 seconds.
Note
A correct measurement can not be obtained if the battery
temperat ...
Mazda 6 Owners Manual: Fuel-Filler Cap
To remove the fuel-filler cap, turn it counterclockwise.
Attach the removed cap to the inner side of the fuel lid.
To close the fuel-filler cap, turn it clockwise until a click is heard.
CAUTION
(U.S.A. and Canada) If the check fuel cap warning light illuminates,
the fuel-filler cap may not ...