My 2009 Mazda 6 battery light comes on with all the other instrument lights when ignition key is turned on then goes off with them all but comes back on several seconds after the engine is started. My voltmeter showed 12.06v at the battery terminals before the key was first turned and 11.58v once the engine had been running for a minute or so. It stayed at 11.58v for several minutes.
I charged the battery for approx 30 minutes with a 10A charger after which the voltage was 14.35v. After starting the car, the battery light issue was repeated but after driving for several minutes, maybe 10, the battery light went off and the voltage was 13+v.
This tells me the battery is OK and the issue lies in the charging system.
What can cause the alternator to seemingly start doing its job only after several minutes? Does it have a regulator that might be faulty?

 

The proper way to test the battery is with a battery load tester. You can do it the old school way using a Hydrometer. These are the only 2 ways to test the health of the battery. I recommend to use a battery load tester.

Charging a battery and having the battery holding volts is not a way to determine if the amps are ther to support the voltage.

See this thread for info:
https://www.mazdaforum.com/forum/maz...e2/#post182197


This is the first thing you must do then move on to the charging system diagnosis.

 

Be aware the alternator is controlled by the PCM. Clearly the alternator is not charging when the engine is running.

Using a scan tool with live data, you can view alternator output in both % and volts, the command % from the PCM, battery voltage & Module supply voltage.