Hi all, I have 2 problems, 1) how to set up the simulation correctly 2) why the prototype (and the simulation) of the charger does not go into trickle mode. I used this SgtWookie's batt_SLA model, modified for my battery: http://forum.allaboutcircuits.com/attachment.php?attachmentid=24235&d=1288998265 I took this circuit of a a battery charger from an old EDN article about February 4, 198X. It was advertised as: "Battery charger snaps from full to trickle" by Kennan C. Herrick ESI Electronics Corp San Francisco, CA I first built it and I was not satisfied that it did not go into trickle mode at the end. I then decided to simulate it as a ltspice model to try to understand what was the problem. 1) Problem: I am not sure how to set the .pulse or tran or anything else that could: -charge the battery from 6V to 7.25V to see why the Q2 transistor does not switch off and stay off until some lower voltage. Q2 should give hysteresis to the whole process. Q1 is there to limit the charging current to 130mA for the fist part of the charge and that works fine on the prototype. On the prototype the charge reaches 6.85V at the battery with I=15mA and Q2 Vbe of 0.6V min. then it stays there forever. As I understood Q2 should switch off and a little trickle current go mainly through R7. The lead acid battery is a Gel 6V 1.2A. ILOAD is there with the idea of discharging the battery first before observing how the charge would go. On the model the max V battery is 6.28V with max I charge of 90mA. Q2 Vbe is min 0.9V, max 1.06V. There are some differences with the prototype but the main thing is Q2 does not go off as in the prototype. 2) Problem: Why Q2 does not switch off ? Thanks for all help.