So my girlfriends 2010 mazda 6 died about a week ago. So I put a new battery, alternator, and belt in it. The car now runs fine but the battery light comes on periodically.

 

First to do is the following:
Using a Diagnostic Tool connected to the Diagnostic connector under the drivers dash check for any DTC(s)
Double check that the battery terminal cables are clean and making good contact with the battery cable terminal.
Carefully look at and check the condition of the ground cable from the battery top the chassis or body.
Using a Digital volt ohm tool check both the batteries rested voltage and charge voltage at idle and then by increases the engine speed to 2000 rpm.

 

So I've checked for DTCs, there are none. I've replaced and cleaned the terminals on the battery. The battery is charging at around 13.5 volts. And I will have to check the ground wire.

 

Did you use the proper Diagnostic tool as I mentioned?
Also you did not tell me the rested battery voltage nor the specif rates of charge again as I mentioned??

 

Yes I used an Innova scan tool. I still have to check the resting battery voltage.

 

Hey did you ever fix the issue? I'm having the same problem.