How long are you hoping to have the thing running from a set of batteries ?
Is space / weight an issue ?
The 9V battery is a poor choise for powering the Arduino. It will not last long.
Depending on how often the heater is on it too will drain the 4 AA batteries pretty fast i think.
space/weight is def an issue.
it will be on intermittently for 60-90 minutes. The "intermittently" depends on the temperature....it will be "on" when at or below a setpoint and "off" when at or above another setpoint. The whole contraption is in a very thermodynamic insulated foam enclosure with reflective mylar interior...so it will be insulated as well as anything on earth, and have a very small space of just a few cubic inches to heat.
The temp outside however will be as low as -40C.
I think the 4 AAs will have sufficient capacity, but if testing turns out that it is not, then I'll up to a 6 pack.
any advice on how to get rid of the 9V and run the arduino on just the AAs?