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: Auto Lock/Unlock Function
WARNING
Do not pull the inner handle on a front door: Pulling the inner handle
on a front door while the vehicle is moving is dangerous. Passengers can fall out
of the vehicle if the door opens accidentally , which could result in death or serious
injury.
When the vehicle speed exceeds 20 ...
Mazda 6 Owners Manual: Dtc clearing procedure
1. Start the on-board diagnostic test mode.
2. First press the POWER button, then simultaneously press AUDIO CONT button
for 2 seconds or more.
Caution
Before clearing the DTCs, be sure to enter all of them displayed
in the on-board diagnostic test mode in the Audio Repair Order Form. ...