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: Illuminated Entry System
When the illuminated entry system operates, the overhead lights, the courtesy
lights, and an ambient light* turn on in the following conditions:
The driver's door is unlocked after the ignition is switched OFF.
The ignition is switched OFF with all doors closed.
NOTE
(Overhead lights) ...
Mazda 6 Owners Manual: Pcm removal/installation
Note
For replace the PCM, Setup the WDS and perform the PCM
configuration. (See PCM CONFIGURATION.)
1. Disconnect the negative battery cable.
2. For R.H.D, perform the following procedures.
(1) Remove the front side trim (left-side).
(2) Partially peel back the flower covering.
3 ...