You need to know what exactly is there and if it has value (the contract, the person's electric bills past two years, and an inspection of the batteries/panels/and roof).

DeWalt's 18V XRP batteries are NiCads and, as such, exhibit all the usual NiCad issues such as "memory" and self-discharge.

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.

Happy.co was far better, frankly, anything is better than Appfolio's inspection module.  

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. 

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?...