As such, I generally test and replace the batteries at least once a year. 

You can get battery powered ones if you don't have power by the door.

If the house does not have power get a Temporary power pole installed outside the house and get battery operated cameras and/or solar ones.The last thing you want is to have your incomplete flip listed on the MLS with a description beginning with “Investor Special”If you can’t be there to check on your flip as often as required you can hire project managers to be your eyes and ears.

WiFi smart locks are great b/c they’re a one-and-done install, but have the downside of needing frequent battery replacements due WiFi using a lot of energy vs something like ZWave to a hub (that’s very low energy like Bluetooth). 

Ultium cells building a factory here to manufacture car batteries.

Bullet proof strategy with no interaction is a lock box that has no smarts or batteries to fail.

You’ll need a skill saw, sawzall and battery drill.

So I had a sump pump battery backup installed. 

Nest Yale Lock- this looks great and seems functional, any troubles other then battery dying?  

A lot of them are designed to run on a big battery; check to see if it can just run from the charger all the time.One drawback is that it may only have a relatively wide-angle lens; as far as I know you can't usually swap lenses like you can with a "real" security camera.Wally World sells a few and the big local hunting / sporting goods store will have more.