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: Schedule 1
U.S.A. and Puerto Rico residents - Engine oil flexible maintenance interval
Use when the maintenance monitor for “Oil Change” is set to “Flexible”. For
details, see maintenance monitor.
Chart symbols:
I: Inspect: Inspect and clean, repair, adjust, fill up, or replace if necessary.
T: ...
Mazda 6 Owners Manual: How to Arm the System
1. Close the windows and the moonroof securely (some models).
2. Switch the ignition OFF.
3. Make sure the hood, the doors, and the trunk lid are closed.
4.Press the lock button on the transmitter or lock the driver's door from the
outside with the auxiliary key.
The hazard warning light ...