I rescued this Sensation mower deck from a neighbor's trash pile. It had a bad engine (had thrown a rod, apparently) but these are the best decks ever - solid, thick aluminum, with a flip-over handle so you can mow either direction. It's a sin to throw out one of these. I planned to convert it to electric but it's taken a few years to accumulate all the parts.
First I got a 24VDC motor on ebay, rated for about 1 HP. I think it's a tank turret motor. But the shaft has gear teeth, is not very big and doesn't stick out very far. A friend in town had some surplus 12V batteries for sale, so I bought two, and he had a look at the motor. He told me that probably the bearings are not beefy enough for a lawnmower; besides the hassle of how to convert the gear output to a smooth shaft large enough for a lawnmower blade adapter. Since I got the batteries, I kept them on float charge in the garage with a couple of these chargers.
Then I found this motor. It seems ideal; it fits the Sensation deck like it was made for it, and even has battery holders molded into the casting. They are for batteries with a 7 x 3 inch base, like the ones that are in my other cordless mower (the Sears one, of Black and Decker design). But the batteries I got are a bit larger, so I had to make extender brackets. Those worked out pretty well.
Unfortunately one of the batteries turned out to be a dud. It reads 12.5V or so but doesn't output much current into a load. So I will need to get another one. The motor is designed for 24V and if I give it only 12V, I don't get a lot of power. It was enough to get a little bit of mowing done, though.
The switch for now is a heavy-duty toggle switch that has a decent DC rating, but it would be better to have a lever grip so that if I release it, the mower automatically turns off. I will try to figure out a way to do that eventually. I discovered that a conduit in-line connection box makes a good box for a toggle switch.
With such big batteries, it's kindof heavy, so I guess I will get some exercise pushing it around.