Update: Running for over 12 months on 2 regular AA batteries using the method I described above. Basically rather than powering the tsl257 constantly, I wake up every 125ms then send power to the tsl257, check if there has been a state change in the power meter light then go back to sleep.

@user2684 I had the same issue when I built this with a standalone atmega328p running on 2x AA's. I set it up with wake on interrupt from the It was constantly drawing 1.6mA to power the tsl257 to detect the flashes. My target was 1+ years on 2 x AA's. My solution to achieve this was to sleep for 125ms, wake up, send power to tsl257 to check light state (on/off), if it changed from previous reading then there was a pulse (well half pulse). By measuring every 125ms I can guarantee to capture fast pulses up to 14.4kW. (3600000/125)/2. It is 20kW max draw for residential in my country. Now:
Average mA Consumption Sleep 0.1
Average mA Consumption Wake 0.064516129
Average mA Consumption Transmit 0.002916667
Battery Life (2xAAs) = 1.7 years