170523-2128 EDT
After some online study, reading the manual, and talking with the Home Depot salesman I bought a 21" push type EGO. Cost with Michigan sales tax was somewhat under $500.
This machine comes with a 5 AH battery. The self-propelled unit has a 7.5 AH battery. The 7.5 AH battery will fit in my machine, but is very expensive. My guess is that there are 14 cells in series. 56/14 = 4.0 V. Just after fully charging the battery in their fast charge charger the voltage was 58.0 V. With the battery unloaded for about 1 hour this dropped to about 57.8 V, 57.8/14 = 4.13 V. After 1/2 to 3/4 hour of use the voltage dropped to 50.0 V and low battery indicator had not turn on yet. I am guessing that my average power load on the battery might have been somewhat under 500 W, 10 A.
Mower performance was very good as would be expected from the reviews. In Consumers Reports this mower is compared with gas mowers rather than corded electric mowers.
Performance of the EGO is vastly superior to a corded mower. My durability experience with several Black and Decker single blade corded motors has not been good. Going back 50+ years the twin blade Black and Decker mower I had given my dad had good durability. It probably lasted in excess of 30 years, was light, and easy to handle. If a comparable one existed today I would like to have one.
EGO's description does not indicate a brushless motor, while at least one battery powered competitor does advertize a brushless motor. Home Depot said the EGO is a brushless. When running the mower I sense very little speed variation with highly different mechanical loads.
I don't believe any of my nearby neighbors have any kind of electric mower. Probably most neighbors have lawn service, several have riding mowers and do their own lawn, and neither of these groups get exercise from lawn mowing. No neighbors have push type gasoline mowers, and a few have gasoline self-propelled and do their own lawn.
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