IMPROPER IN-FLIGHT PLANNING/DECISION BY THE PILOT, AND THE ACCUMULATION OF AIRFRAME ICE, WHICH RESULTED IN AN INADVERTENT STALL. FACTORS ASSOCIATED WITH THE ACCIDENT WERE: PARTIAL FAILURE OF BOTH ALTERNATORS, WHICH RESULTED IN A SUBSEQUENT ELECTRICAL SYSTEM FAILURE AND AN INOPERATIVE ANTI-ICE/DE-ICE SYSTEM, ADVERSE WEATHER (ICING) CONDITIONS, AND AIRFRAME (WING) ICE.