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: Lights-On Reminder
The lights-on reminder is operable when the time setting*1 of the auto headlight
off function is off.
If lights are on and the ignition is switched to ACC or off, a continuous beep
sound will be heard when the driver's door is opened.
*1 If the light switch is left on, the auto headlight off f ...
Mazda 6 Owners Manual: Advanced Keyless Entry System
WARNING
Radio waves from the key may affect medical devices such as pacemakers:
Before using the key near people who use medical devices, ask the medical device
manufacturer or your physician if radio waves from the key will affect the device.
The advanced keyless function allows you to lock/u ...