over here in Germany we have a lot of Scale/Semi-scale-aerotowing-action and most of the gliders have a retract (if the full-scale has one as well).
But I donít know anybody who uses a second battery-pack just for the retract (of course there may be some guys who do it, that I donít know of) in their gliders. Seems to me, that itís an american issue ...
To tell not only from my limited personal experience I can say, that I observe closely the german messageboard RC-Network
and participate on an almost daily basis there from day 1 in 2002 especially in the glider/scale-glider-section and I canít recall any substantial discussion on this topic.
Tonys observations are very accurate and true without doubt.
But I think, that if you have a good servo (metal gear, enough torque) with a good linkage and an appropriate door-opening-and-closing mechanism (there are various methods) and you keep an eye on the mechanism during the season and do a little maintenance here and there (removing debris, controlling smooth operation), you donít need a back-up-system just for the retract.