The airplane nosed over during a precautionary landing in a soft, dirt field. The pilot and a mechanic had been ferrying the airplane back to its base after replacing the starter and battery solenoids, and the battery. The pre-flight run-up had revealed no problems and the ammeter had indicated a 'full charge'. According to the pilot, about 30 minutes after departure, the interior lighting began to dim and the airplane electrical system failed. The pilot was subsequently unable to locate the destination airport or an alternate; he then became concerned about running out of fuel and elected to make the precautionary landing. Post-accident examination of the airplane electrical system by the FAA revealed that the alternator had failed internally and that the battery was completely discharged. The inspector also observed that the alternator 60 amp circuit breaker was 'popped'. The pilot reported having approximately 5 hours total night flight experience, approximately 1 of which was obtained in the last 90 days.