I have been flying with an Ultralife UBBL09 Li Ion battery for several
years now with very good results. This is a military grade battery
and built to very high standards. It comes integraded with 12 and
24VDC output from the same battery and also has LCD charge
indicators. Because the Li discharge curve running flat at 11.1, I
run the battery at 24VDC with a 12VDC voltage regulator to maintain
constant voltage to the radio to improve performance. The transponder
takes 24VDC, so I don't need to regulate that. Other instruments are
much less sensitive to voltage. I run a 4700, 302 and transponder and
go on multiple day 8 hour cross country flights without recharging.
The only draw back is the insane price for the battery and charging
system. I am contemplating upgrading my panel to all glass and will
add an additional UBBL09 to power all the electric instruments.

-Christian Mackin
ASW-27 #33