Costco has a Greenworks 80-volt, 21-inch self-propelled mower deal with discharge bag, two batteries and a charger. The bigger battery delivers about 45 minutes of mowing while the smaller battery delivers about half that. I use mine in mulching mode on a very hilly yard and can attest to the power reserve the batteries have. This is my third season with the mower.
The package is listed at $629 at the moment, but Costco has offered it at a discount in the past.
Greenworks' customer service reputation hasn't been great, so I like buying from Costco, where I can take it back for a refund if I'm not happy. Fortunately, the mower and batteries have not disappointed.