In the past I have built a number of 12V lead-acid battery chargers. Most of them were used on SLA type at or near room temperature. I decided to try building one with built in temperature compensation. I remember copying the attached schematic from this website. I built it today and I am impressed with the temperature compensation provided by the 2N3904(Q2) I have a fluke 87-V with a bead temperature probe and used a fluke 8062 DVM to measure the voltage. I fastened the bead probe and the 2N3904 to a 20W 20 resistor, with black cable ties. Room temperature was 32.2° C and the output voltage was adjusted to 13.65V. I applied 6.1VDC @ .29A to the resistor and monitored the temperature rise. The results were 42.0 C output voltage 13.46. 47.1° and output voltage 13.35V. My calculations show that the average change in charge voltage for a float charger/C° is 20mV. My question is: Is this the recommended change in charge voltage for the SLA battery?