The pilot reported that, he departed normally to fly the airport traffic pattern. After he turned to the base leg of the traffic pattern, he observed a low voltage indication on the annunciator panel and was unable to announce his base turn on the radio. The pilot then turned to the final approach leg of the traffic pattern without making the announcement on the radio and added three notches of flaps. He experienced “windshear” near the runway threshold and the airplane briefly ascended. The pilot attempted to regain his glide path by extending full flaps and the airplane floated down the runway. At the time he was concerned about climbing out, so he elected to continue the landing instead of performing a go-around. After the airplane eventually touched down on the runway, the pilot applied full braking, but the airplane skidded off the runway edge into a ditch, which resulted in substantial damage to the right wing. According to the pilot, he misjudged the landing distance and landed long to salvage the landing instead of attempting a go-around. He further remarked that the electrical issue affected his radio and prevented him from announcing his base and final turns in the airport traffic pattern, which may have influenced his decision to land promptly. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.