In theory it looks fine, and accrording to my calculations, 2xAA cells should be able to drive the EmonTH for about 9-10 months with the DHT22. Assumptions: old booster setup, 2s uptime at each measurement, 1-minute intervals, about 28 uA sleeping current (7 uA [email protected] + 7 uA booster, 50% efficiency), and about 10 mA average wake including 95% efficiency current including transmission. Yet you only seem to have 7 months. Naturally it’s a short span and a relatively high average consumption so 2-3 months theory vs. real lifie is not very big.
However, if you use any of the modern chips, their consumption is practically nonexistent. In that case, without the booster you can go down to about 1.9V or 0.95V/battery, but let’s be safe and say 2V. Standard specs are down to 0.8V usually. That’s about 73% of nominal mAh, 2200 mAh for an AA cell (3.1V - 1.6V vs. 3.1V - 2V). Assuming no booster, 7 uA sleep current, 50 mA wake current with transmission, 10 ms wake time, 1 measurements/minute, we get 14 years. There is only one kind of battery that lasts that long, the lithium primary. They’re 1.5V and a little more expensive. Every other kid of battery needs to be replaced in 3-4 years at most. No booster can help with that. Since a booster is not free amperage-wise, it wouldn’t prolong the lithium battery usage either.
Brown-out is not a problem, you can set it as low as you feel comfortable. In practice, 8 MHz is good down to ~1.8V.
Calculator I used: http://oregonembedded.com/batterycalc.htm
Well, just my 2cents.