I'm occasionally boggling that there's no electric farm equipment, since it at least suffers from one fewer problem than electric cars: you're mostly driving around in a finite area. You might need to plumb a dozen or so charging stations at various fields, and have the equivalent ability to essentially carry a five gallon jug of electricity to a tractor in a field when you run out accidentally, but you're not driving 200 miles to an Ikea on the spur of the moment.
Besides the lack of consumer demand (farmers have other things to worry about), I think the other thing that makes the farm market slow to adopt electric is that the market is, erm, slow. People are constantly buying new cars. Some people drive a new car every year, some people drive a car for 10 or 20 years, but I'd guess that most people get a new car every 3-7 years. That means, firstly, that a lot of people have bought a new car since they first started getting good; that also means that an electric car only has to last 3-7 years to meet most people's expectations, and your car will only be 3-7 years out of date when you get a new one.
I would guess the average farm tractor in the fields today in the US is 20-30 years old. You've got some really new ones with GPS, autopilot and satellite TV, sure, but you've also got some 50-75 year old tractors which are still doing just fine. I used to rake hay with a little Farm-All my great grandfather bought back in his prime, which is still going strong today, and I bought a used Cletrac from '45 to use around my woodlot.
This creates three problems for the prospective electric tractor manufactures: not a lot of tractors are sold each year, so you're fighting for a chunk of a very slow-moving market; prospective buyers are going to be asking themselves "will this tractor outlive me?" so you need to have a compelling story on how those battery packs and motor bearings are going to last 50 years, or be easily replaceable; the technology is still rapidly developing, so you also need to explain to the prospective buyer why it's is worth buying an electric tractor now, instead of waiting 10 years to buy a more mature electric tractor.