Can you add some step up / step down regulators to your power options? I often end up needing to order some of these, some similar regulators would be great:
https://www.pololu.com/product/2122
https://www.pololu.com/product/2123
https://www.pololu.com/product/2561
https://www.pololu.com/product/2891
This is a mirror post of the one there: viewtopic.php?f=103&t=54776
That would be extremely useful for projects that rely on primary batteries over a wide range of temperatures and with varying loads, in which case the battery voltage can fluctuate quite a bit.