I already check the generator/altenator and the battery, it seems working well after the oreilly pass the tester. Suddenly turns on and after a couple of minutes it turns off.

Ideas?

 

did you measure voltage at the battery with the engine off and with the car running at a fast idle? Battery engine off should be about 12.6 V, car running at a fast idle should be 14V-14.5V. Next is try adding all accessories - AC blower, rear defogger, high beams etc. Voltage should stay over 13V.

 

Check for loose or dirty battery cable connections too. The Volvo is super sensitive to the correct voltage.

 

Mine did exactly the same. After driving 10 minutes or so, the message would appear and the battery light came on then it would go off after a while. It started taking longer to go off. Using Dash Command on my iPhone and a WIFI OBDII adapter, I monitored the battery voltage while driving. The voltage would run around 14V then drop to 12V and the message would appear. The voltage would go back to 14V and message would go away.

Replacing the alternator fixed the problem. I might have gotten away with replacing the regulator only but the alternator had nearly 200K miles. Bearings and brushes would probably be going soon.
Stan