I had been meaning to test my devices on battery to see just how long they would last. I recently got that chance by mistake.
My application has a Boron LTE connected to Particle Cloud, checking OneWire sensors every 20 seconds, and publishing to the cloud every 20 minutes. The device does not sleep at all.
Recently I installed some at my pilot site, and I overlooked the fact that the USB connector wasn’t soldered properly on one, so it only operated on battery. Each device has a single 18650 LiIon 2200mAh cell from Adafruit connected to the LiPo pin on the Boron LTE. Now, this was unfortunate in that I now have a dead device 500 miles away that can’t get power. But the happy part of this accident is that it remained powered and reporting to the cloud for more than 72 hours! I originally was hoping for 24 hours on battery, and it’s exceeding expectations. Now to build and ship a replacement for the fauly device… 
EDIT: The 40+ hour runtime was with a cellular connection with signal strength of < -120 dBm. Even more goodness.
EDIT 2: Oops, I got the runtime hours wrong. It wasn’t 40 hours, it was > 72 (more like 84) hours runtime on that single cell. Wow!