If your plan is to operate a Mode-S with ES transponder, or a UAT Out along with Mode C transponder to comply with the 2020 mandate, along with a low wattage Comm radio, I would suggest that your lightest option would be a light weight solar charger and either a Lithium Ion or Lithium Polymer battery pack. The solar charged LiPo combination gives you a lot of useful time with the avionics necessary to fly in your area without a huge weight penalty.
Caveat: The Lithium Ion and especially the Lithium Polymer batteries can be a fire danger if discharged too rapidly (heavy loads like a starter) or in a crash scenario if they are punctured. However, when I was working in the UAV/Drone world we used Lithium Polymer batteries exclusively and had some very high G impact crashes. The only damage we ever saw with the Li-Po batteries was heat damage from discharging them too rapidly running electric motors on the electric UAVs. While there are now Li-ion and Li-Po batteries available for aircraft, at this time I don't recommend them as the primary battery for an aircraft with a complete alternator/battery system. Thermal damage from improper or high charge rates is also an issue with these batteries. -Jeff Scott Los Alamos, NM > Sent: Tuesday, July 15, 2014 at 7:36 AM > From: "Mike via KRnet" <krnet at list.krnet.org> > To: "'Dan Heath'" <danrh at windstream.net>, 'KRnet' <krnet at list.krnet.org> > Subject: Re: KR> "Engine-driven alternator?" > > That's what I had with my solar panel system. My A65 had no alternator so I > had one 9Ahr Yuasa battery online (powering my radio, intercom, gps etc) and > a back-up 3Ahr one off-line being recharged by the solar panel. This panel > was a low profile monocrystalline 12vdc 5.2 watt unit that worked on cloudy > days and even under the sky lights inside the hangar. See > http://tinyurl.com/aooqfv > > A small digital voltmeter monitored the condition of the online battery and > I used a DPDT switch to bring the recharged one online and redirect the > drained one back to the solar panel. >
