It's a 10 year lease agreement. You pay them, and when the 10 years is up you have to return the batteries. At no point does the customer own the batteries.

It's like leasing a car, except with a car lease you have the option to pay extra to buy it out at the end and take ownership; with this lease agreement you don't.

This is like leasing a car except that the dealership can show up with other customers to take "your" car for test drives or just to drive it around for any other reason whenever they want to, for however long they want to, and they won't pay you back for any of the gas they use. Basically turning your personal garage into their distributed showroom.

IIRC pre-covid when the program was quite new, customer could buy the batteries outright. Later on they added the lease option.

One of the issues with these is the limited storage capacity. While it is nice for short outages, there are sometimes multi-day events in the winter. I think the longest was in the late 90s from an ice storm and was over a week. If you have solar, less of an issue but not everyone does (though solar does have surprisingly good install base in Vermont).

I've not checked to see if GMP limits the install locations but do recall some states/munis trying to limit them to outside the home due to fire risk.