THE CONCLUSION FIRST:
The winning lawn mower for me was the Kobalt 13-Amp 21-in Corded Electric Lawn Mower (model #KM 211-06).
For the last three years, I've been mowing with an early generation 40V cordless Ryobi. But in the last few weeks, I could no longer finish my lawn on a single charge and Ryobi changed their battery style. So it was time for a new one.
For me, I wanted electric/battery because of both the hassle of gas engines and the noise/smell/pollution factor. I recently heard that running a lawn for one hour emits as much carbon as running a modern car for 40 hours. Crazy if that statistic is correct.
I started my search by trying the Dewalt 20V dual battery in hopes I could have an entire power and garden tool selection that used the same battery technology. Well, the lawn mower didn't cut it (literally). It would get overwhelmed and turn off every 30 seconds with medium long grass. So back to the store it went.
When I returned the Dewalt, the nicest customer service person at Home Depot told me that he sees all sorts of cordless mowers returned. He said the only manufacturer that barely ever gets returned and is worth getting is the 56V Ego. But Home Depot no longer carries Ego. He actually recommended I leave Home Depot and go to Lowes or Ace to get the Ego. That's how much he believes in it.
I've also been curious about the 80V Atlas mower at Harbor Freight. It gets great reviews on their website but they sell the battery and charger separately from the mower, and the batteries are currently out of stock.
I then was curious about corded mowers. It's a little more tricky dealing with a cord but I had an accessible outdoor power outlet and long enough extension cord to do my entire lawn. With corded, I know I'll have plenty of power and not have to worry about battery overload.
I researched the Black & Decker and Kobalt corded models. I went with Kobalt because it had a 21 inch cutting deck that was made out of steel. It seemed more durable than the Black & Decker. Both models were also half the price of the entry level battery mowers at $200 vs $400.
I've been mowing with the Kobalt for a couple weeks now and I must say I am pretty impressed. The mower has consistent power, good cut, and three options for handling the grass (mulch, bag, side discharge). And I didn't mind the cord. It's kind of like a vacuum. I just mowed in a way where I never had to cross the cord.
If you can deal with the cord, there are so many advantages over battery. First, it has no issues with power. Battery powered mowers can get overloaded but that is rarely the case with corded. Second, the mower, if made well, will last longer. Batteries deteriorate over time so you will likely need to replace the battery every 3-5 years. And if battery technology changes like it did in my case, you'll need to replace the entire mower.
Lastly, batteries are not that environmentally friendly. There are studies going on now that show it takes more resources and carbon emissions to make an electric battery powered car than a car with an internal combustion engine. Over the full life-span, the electric vehicle then uses less because it requires cleaner electricity to power it than gasoline, but it's not that much better. And you also need to figure out how to recycle the batteries to keep them polluting the environment. I'm sure the same principles apply to lawn mowers and other powered equipment.
It's too bad because very few manufacturers focus on corded options. They are all jumping into the battery powered game leaving few corded options. What it will take is more people buying and being interested in corded options for things to change.
But I will agree that corded lawn mowers won't work for everyone. Battery powered mowers do have there advantages. If I had to go with a battery powered mower, I would go with either the Ego or Atlas models. I personally would choose the entry-level models without the self-propelled feature because that option uses battery power and I have a pretty flat yard that a push mower can handle.