I don't see why power would be an issue. Why do you even assume there's a huge battery instead of a diesel engine and generator? Having this thing be autonomo

I don't see why power would be an issue. Why do you even assume there's a huge battery instead of a diesel engine and generator? Having this thing be autonomous makes it more expensive to acquire, yes, but way cheaper to operate because the labor cost of pulling this thing with a non-autonomous tractor is quite large (even if the tractor were autonomous, having two autonomous robots doing different things is better than having one doing two different things that might halve its availability for each kind of task). This is a very big deal. If labor were a non-issue we'd have people weeding manually and we'd not use herbicides. Everything in farming is about labor, which is why we've gone from being agrarian societies to industrial and post-industrial ones: by bringing economies of scale to agriculture in order to greatly reduce labor costs in agriculture.