I've also welded a broken top link on a bush hog with 3 car batteries and jumper cables in the field.

They may also require batteries to start or manual lighting.

It's really not rocket science to screw in a battery-powered trail camera in a steel case next to the front door and another one next to the back door.

Great flashlights and extra batteries that fit, super long extender ladder, korkers/or other brands over shoe to go over your steel toe boots, GFCI tester, moisture meter, a dog nose, an extender mirror, shovel to check foundation moisture, respirator as some properties have gross smells or chemical exposure, regular retractable tape measure forget the laser one, 5 gallon bucket, zip lock baggies, brown paper bags, putty knife, variety of screw drivers,Are you checking basements?

In all the leases I am clear the batteries are the tenant's responsibility and make sure to tell them if it blinks red it's time to replace the battery. 

The law allows you to charge rent up until the new tenant took over.

Blink is an Amazon company and they have wireless, battery operated cameras with motion detection at a very high quality and relatively low cost. 

What would you charge to diagnose dead batteries in a thermostat.....$75 trip charge?...

The Ring is nice because they have a battery operated one so thieves can't cut wires.The Nest is nice because the interface for reviewing/saving videos is easier to use in my opinion.We use both.Mike

I can only imagine how many calls you would get asking to be bring keys to let a tenant in because the battery is dead in a smart lock or some other issue (and I have smart locks on my personal home, just none of my rentals).