I would have bought the kit just for the charger and batteries, and I deeply regret that I didn't. My parents actually bought the kit and the mower is very nice for taking care of what the robot can't reach.
I know you can get chinesium batteries for cheap, but I have a bit of respect for these things. Tool batteries get dropped, used as hammers and abused to the point of thermal foldback. Then once you've depleted a battery, you put it on the fan cooled charger. I kinda want to stay genuine here to avoid fires and other unpleasant things. I also always make sure to never leave a battery in the €27 knockoff impact gun I got.