That's not QUITE true, according to the Concorde engineer that helped me
write the series of Kitplanes articles on AGM charging.

The AGM chemistry likes to be cycled. That is, the battery likes to be
taken up to 13.4 volts, allowed to self-discharge back down to 12.6, back up
to 13.4 and so forth. The cycle time is measured in days or weeks,
depending on how much "keep alive" circuits (clocks, radio memories, etc.)
are sucking on an "off" battery.

Jim




So, extrapolating for the charging voltage in flight, I would suggest
26.5 volts... And I would consider adding a charge maintainer for
sitting idle (stops the plates from sulfating) that puts out something
near 24.5 volts......

denny