Your symptoms are exactly what I would expect if one or more of the rectifier diodes in the alternator have failed. This is a common alternator failure mode (not just for Volvos, but for every other make and model car as well). Your Dealer, or even local Sears Roebuck, should be able to check this with an oscilloscope. There will be obvious missing phases in the alternator output ripple waveform during charging if any diodes have failed. Memorize that last sentence, and recite it to the customer service rep at the Dealer . . . that will get their attention.

Regarding rotor warpage - it is most often due to one of the following two causes:
(1) Resurfacing as part od a "brake job". This is where some of the metal is removed in order to restore a perfectly smooth surface.
(2) Improper procededure tightening wheel lug bolts (the 5 bolts that hold each wheel on).
Just before you noticed the syptoms of warpage, did you have brake repairs or tires rotated? Or a State safety inspection (In my State, the inspectiors are famous for removing a wheel to check brake condition, then damaging the rotors when replacing it)?