Tinpilot,
Thankyou. That was probably the glider I passed yesterday.
I asked the question because after what I think was about 7.5 hours flying he still had enough electrical power to speak to an ATC radar unit and to use a transponder with mode C, which helped us to see and avoid him, using our TCAS to assist our lookout.
Good on him, a good example of how to fly in a thoroughly professional manner, he allowed us the chance to avoid his aircraft by changing our transit altitude in good time and keep us all the safer for it, whilst maintaining my passengers' comfort.