The flight instructor reported that he was building hours in the powered glider in preparation for his glider instructor rating examination. He departed the airport with power and climbed to the west to chase thermals. After reaching 4,000 ft. above ground level (agl), he shut down the engine, left battery power on, and continued to climb to 4,500 ft. After 30 minutes, he attempted to restart the engine, but the starter only cranked the engine briefly and the propeller travelled 1 full revolution then stopped. After another unsuccessful engine start attempt, and too far away to glide back to the airport, he located a field for a forced landing. During the landing roll, the main landing gear wheels dug into the soft field and the glider nosed over, coming to rest inverted.

A post-accident examination revealed that the single battery was depleted as it powered the avionics during the non-powered flight. Its depleted level was insufficient to power the starter during the engine restart sequence.

The powered glider sustained substantial damage to the engine mount truss.

The pilot reported that there were no preimpact malfunctions or failures to the airframe or engine that would have precluded normal operation.