This thread started with regard to an aircraft on battery power. Transponders are heavy power users and expensive, so impracticable in this case. No one has mentioned the NATS Eva project. The purpose was to identify the need of and specifications for low cost conspicuity: low cost and a low power demand was the overriding aim. FLARM, Trig, funkwerk and Pilotaware have produced an interesting array of units, utilising ADS-B and which do not demand a lot of power. They vary in price between £250 and £2,500.
Perhaps some pilots with a practical knowledge of this stuff may join in, otherwise I would suggest contacting the LAA who have a considerable and necessary expertise.
Last edited by Fl1ingfrog; 3rd Dec 2019 at 21:26.