Battery life experiences

I am using a few esp32 boards connected to either an ntc probe or dallas temp sensor. My goal is to monitor things like boiler flow and return temps.

Configuring the esp32 (I initially started in arduino ide before swithing to esphome) is relatively straightforward but I need these devices to be battery powered and this is where I am struggling.

I initially started with some 16wh usb power tanks. These work fine until you use deep sleep at which point the power tank goes to sleep and the device doesnt wake.

I then bought a couple of 18650 batteries (molicell P28A) and some battery shields off ebay. This eliminates the deep sleep problem but I am only seeing a capacity of 6-7wh against a spec of 10.3. Even with deep sleep these are running out within a few days.

I have been using a deep sleep period of up to 5mins with a wake period of 5s. This seems to work ok but the battery life is still poor.

What kind of real world experience/life are people getting with battery powered devices and should I be looking at a difference battery/shield combo to get reasonable life (I would like it to last 30-60 days between charges)?

Not sure if my battery shield is the problem, it appears to stop charging at 4.05v instead of 4.2?

Firstly, esp32 boards perform very differntly. You want one with very little quintescent current

Or build your own of a bare esp32/esp8266 chip (later uses less power).

That should somehow even work out with encrypted wifi and a reasonable deep sleep interval.

Otherwise - if you want a long runner try something like esp-now which significantly can reduce the run time.