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: Essential Information
Introduction
Be careful not to hurt yourself when inspecting your vehicle, replacing a tire,
or doing some kind of maintenance such as car washing.
In particular, wear thick work gloves such as cotton gloves when touching areas
that are difficult to see while inspecting or working on your vehi ...
Mazda 6 Owners Manual: Rear door speaker inspection
1. Inspect for resistance between the rear door speaker terminals using an
ohmmeter.
If not as specified, replace the rear door speaker.
2. To verify that the rear door speaker outputs sound, apply voltage to the
rear door speaker and release using a 1.5-V battery.
If not outputs ...