Problem: I need to design a thermostat that keeps a silicone heater at 39C +/- 1C for 15minutes, powered by 6 x 9V batteries (series or parallel). (Or should it be AA batteries? Batteries to be exhausted after 15minutes.)
I've concluded that this is nothing more than a very specific Frankenstein version of a thermostat.
The area of the silicone heater needs to be roughly 12square inches.
I've got so many amps, volts, ohm equations, and thermometers and breadboards that i've burnt through, that I'm actually at that point where I'm willing to give someoen $1000's to build it for me, because I've wasted enough time and money on my own doing the guessing game.