Last weekend, I gave up on trying to repair at least one of my two gas mowers. I replaced a plug, pull cord, changed oil, cleaned carbs, swapped gas (thinking it was bad), cleaned combustion chambers, sharpened blades, etc. I gave up after 12-14 hours into them and found on Craigslist, a lightly used Greenworks 40V lawnmower with two batteries and a charger for less than half of what they are new. It was ~120 miles away, but close to a Supercharger so I took a nice road trip. Got it home, pushed the button, pulled the lever and the thing cranked right up. I didn't even feel the need to put on hearing protection! It finished the lawn in no time flat!
Knowing how Tesla keeps their LiON batteries healthy, I'm going to keep the lawnmower batteries charged at 75% (3/4 lights) and in a cool room. When it's time to mow, I'll charge them up to 100% and make sure they don't run down too far.
Now, the only thing I have that uses gasoline is my Volt. It rarely uses gas, so I don't feel too bad. It will probably be replaced by a Model 3, soon enough.