Alert when low/dead sensor battery/no sensor reading?

I’ve got a bunch of battery powered sensors, and most of them either don’t include battery level in the sensor packet, or permanently shows low battery when I use rechargeable batteries in them, so the only way I know for sure to know they are dead and need fresh batteries is if they just don’t send a signal within a couple hours/days.

I’m guessing I’m not the only one wondering how to solve this, but google failed me, and I’m new to homeassistant.

Any tips on how to get started on an automation for this?

Not a solution but an FYI for those who may discover this in the future.
Alkaline batteries start off at 1.5 volts that drops until the device no longer powers the device. That “gone dead” state for some devices can be 1.2 volts. Fully charged rechargeable batteries START at 1.2 volts and have a very steady delivery until a sudden drop off at the end of their charge. That is for typical AA or AAA sized batteries, but other types will have similar voltage differences between the rechargeable and disposable.

Nice, though I’ve seen some rechargeable batteries start at around 1.5 V and drop “rapidly” down to 1.2 where they stay a long time before they finally drop to less than 1V.