Hi Pete, have tried pout this circuit and sob sob sob sob, it doesnt work, I have made it exactly the way you denoted but the RED Led comes on and cuts off the charging, the charger voltage is set to 13.8v without the zener connected, and the moment the zener is connected it drops off!!!! what do I do now, also the funny part that I noticed is if the zener is not connected and I touch it with my finger the RED Led comes on and stops charging, funny but true, so what is it that you can please help me with now, the circuit for sure did look very promising but hasnt yet worked, also some points I would like to tell you the batter used was a AMPTEK 12V7.6 SLA and transformer was 18-0-18 1.5 Amp, the battery post discharge showed voltage as 12.42 and on full charge generally shows around 13.10. Please guide your help is utmost required.