On April 6, 2011, about 2045 central daylight time, a Mooney M20K airplane, N305M, ditched into Lake Pontchartrain following a complete loss of engine power after takeoff from Lakefront Airport (NEW) near New Orleans, Louisiana. The private pilot and passenger were not injured. The airplane sustained substantial damage to the fuselage and wings. The aircraft was registered to ALC, LLC, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. Night visual meteorological conditions prevailed for the flight, which was operating on an instrument flight rules (IFR) flight plan. The flight was originating at the time of the accident. The intended destination was Atlanta Regional Airport (FFC), Atlanta, Georgia. A line service employee at the local fixed base operator stated that the pilot attempted to depart about 1400. However, the pilot was not able to get the engine started due to a dead battery. At the pilot's request, he connected a ground power unit to the airplane and the engine started. However, the pilot returned about 5 minutes later noting that he could not get any lights on in the cockpit. He relocated the airplane to the hangar, and a mechanic removed and charged the battery. After charging was complete, the airplane was removed from the hangar and the engine started with the aid of the ground power unit. After an engine run of approximately 10 minutes, the pilot indicated that everything was working normally and subsequently departed. The pilot reported that the airplane engine was started using external power. He completed the applicable preflight checklists and departed without difficulty. During initial climb after takeoff, he noticed an over voltage indication. He informed air traffic control (ATC) and elected to return to the departure airport for landing. The avionics began to flicker and eventually the electrical system failed completely. After identifying the airport, he began to manually extend the landing gear. Upon approaching the airport, the landing gear was not fully extended and the pilot turned the airplane to parallel the runway and level off. The engine subsequently lost power and he ditched the airplane in Lake Pontchartrain. The pilot and passenger successfully exited the airplane and swam to shore for assistance. The passenger stated that several minutes after takeoff, an indicator light illuminated. Immediately after receiving a heading to the airport from ATC, the panel lights flickered and went dark, and the intercom system failed. The pilot attempted to lower the landing gear by using the manual gear extension lever located between the pilot and passenger seats. As they approached the runway, the pilot directed the airplane to the right out over Lake Pontchartrain. The airplane continued to descend and they landed on the lake. They were able to exit the airplane and donned their life vests as the airplane submerged. The airplane was recovered from the lake on April 21, 2011. A postrecovery examination did not reveal any anomalies consistent with a preimpact failure or malfunction. The alternator circuit breakers (ALT 1 Field and ALT 1) were open at the time of the inspection; however, no discrepancies related to the alternator or circuit breaker installation were observed. Further inspection of the electrical system revealed slight damage to a single wire common to a firewall cannon plug. The damage did not compromise the wire conductor. The wire bundle exiting the cannon plug was routed to a 90-degree bend. These discrepancies were not consistent with a complete loss of electrical power. No other anomalies related to the electrical system were observed. During the postrecovery examination, the engine exhibited internal continuity via crankshaft rotation. Compression was obtained at all cylinders. Engine rotation produced fluid at the fuel control unit inlet line consistent with operation of the engine driven fuel pump. The air intake duct assembly and air filter appeared to be intact. The points on both magnetos opened and closed when rotated by hand. The engine throttle was in the idle position, with the propeller and mixture controls in the forward positions. No anomalies consistent with a loss of engine power were observed. Operation of the engine ignition system is completely independent of the airplane electrical system. The most recent annual inspection was completed on August 6, 2010, at 891.9 hours recording tachometer time. An engine oil change was completed by the pilot on January 2, 2011, at 957.3 hours. A maintenance entry dated the same day as the accident noted recharging of the batteries and an operational check. The recording tachometer time was 970.6 hours. The airplane was fueled with 42.1 gallons of 100 low lead aviation gasoline prior to departure. Sunset occurred at 1922 on the day of the accident, with civil twilight ending at 1946. The moon set at 2225. The moon was in a waxing crescent phase with 9-percent of the disk illuminated.