If you're using a keypad lock, what if the batteries die and they can't get it in? 

Specifically a Tesla charger. ??

A third use is lead acid for batteries.

Any suggestions for an inexpensive preferably battery operated intercom/doorbell?  

The only thing to consider is the batteries need to be changed every three months and it requires internet access to operate.

Those batteries are not cheap and have short life-spans.

KORE Power, which was founded in 2018, said this would be the first lithium-ion battery manufacturing facility owned by a U.S. company.In addition to the 3,000 would-be KORE Power employees, the company estimated that the new plant would bring an additional 10,000 direct and indirect jobs to the selected region.

We charge rent at $2,150 per month and mortgage payment is $1560.

You charge rent.

I most likely would get the electric battery powered ones that are now available.