It generally takes about 14.2V to charge a conventional lead-acid battery fully, but modern voltage regulators can get pretty sophisicated. Most 12V accessories don't last as long with a high voltage.
A test of the charging system is to monitor the voltage across the battery at idle, then turn on the lights (high beam & fog). The voltage should stay about the same. If it drops by 1/2 Volt or less, increase the rpms a bit and see if it goes back up. If you have any suspicions after these tests, have the charging system performance tested.