Sorry for the slow reply - but unused threads now lock automatically after a certain time, to prevent people posting in them as has happened in the past.
I was never able to find one, and I looked before I started tracing the voltage setting part of the circuit out. However, the secondary side of a switch-mode regulator is pretty simple - and reverse connecting a battery to the output would presumably blow the rectifier diode, or something in series with it.Actually, it's you I need to ask the question of. Do you know if a schematic is available for that circuit? I used it as a battery charger and accidentally connected a 12V battery with the wrong polarity and something broke.