Bought an Ego LM2135SP This past spring, would never go back to gas. It's self propelled but I dont use it because the mower is so light to push on our nice thick lawn I actually enjoy the small bit of a workout. But it's there for those once in a while times.
New house, new mower, no gas to play with or buy, no oil to change, no air filter, no spark plug and best of all, no smell of gas in our two car attached garage. Also nothing to start, just push a button and go. Yeah, the batteries are expensive but a blanket statement that they go in two years is laughable. Ours has a 3 year warranty and being its top rated I am sure it will last longer.
But even then, the trouble free convenience is worth it to some, including me.
Considering there is no maintenance on the mower, considering its easy and light to push, considering it folds up and can stand up on two wheels in your garage, considering it is easy as heck to take out of the garage and push a button to start mowing and nothing else needed is well worth it to me personally.
Yeah, if the battery fails, IF, the battery fails at the 5 year mark, the cost to replace it is nothing more than what many of my neighbors pay a lawn service to cut their lawn for 6 weeks. Then throw in I never have to buy parts and gas for a standard mower and the cost comes down to less than 6 weeks of a landscaper cutting your lawn for a battery.
It's a luxury I enjoy.

... and its really soooooo cool and quiet ... I like exercise and for me personally after cutting lawns for 50 years, it is the ultimate... oh and let's not discount the cool operation. WOW, no heat coming off the engine like it does with a gas engine is really cool too.