I go to a pool for exercise and the one woman there has an electric scooter. If she drove into the pool, would it pose a hazard to the people in the pool because of the battery.
No.
Unless the battery is a sealed non spillable battery it could leak acid into the water which is dangerous.
I dump battery acid into my pool by the quart…
Maybe a science person on the board will do the math for you. The acid from a battery or two diluted in the volume of a whole pool is going to hardly affect the acidity of the water at all. The current will flow between the two terminals and not electrify the whole pool. The hydrogen and oxygen gas created by electrolysis will not be enough to fill the room and explode the building. The whole scooter landing on top of you could trap you on the bottom and make you drown I suppose.
Being an electric scooter user (as well as wheelchair user) myself, I’d be a lot more worried about the electronics shorting out. I don’t have any cites, but it is my understanding that sealed batteries are almost de rigueur these days (consider that it is possibile to tip over a scooter if you are a klutz - I am my own cite for klutzy behaviour on scooters! :D)
ETA Oops - I think you meant driving off the edge rather than down a slope into the pool; if that is the case shorting out the electronics probably doesn’t matter much; she ain’t getting out without A LOT of help anyway! 