We now install the ones that have 10 year lithium batteries.

Do inspections every 6 months, but just put on the notice of entry that you will be entering to check smoke detector batteries and check for any plumbing leaks, and to please let you know ahead of time if there are any other maintenance issues you should look at while you're there. 

Look at the grid as a giant battery.

I had one way high in the loft that kept chirping even when the battery was replaced.

If it wasn't the govt, I wouldn't put up with it.Tenants will be okay with you coming in to check their smoke detector batteries and check for leaks every 6 months. 

Also, I used to run the Skype app on my iPhone 4S and it really drained my battery towards the end of the day, so that's a concern too.  

Go ahead and post your notice to enter to check the smoke detector batteries, then enter.Why don't you try calling or texting them to ask what's going on?

And an additional $3,000+ if they are seniors or disabled.http://www.sfrb.org/Modules/ShowDocument.aspx?

I did have fans going using my car battery as a power source and I even have a house with raised ceilings...built before a/c existed...and the heat was still unrelenting. 

I drive a 2000 Toyota Tundra that has never given me any trouble.I would avoid hybrids, especially in the price range you're thinking of, as there is a very strong chance you'll be replacing batteries soon and that's VERY expensive.