As has already been pointed out, that is not a 40Ah battery.
In fact, the page has at least two contradictory capacities--it is titled as a 20Ah battery, but the "specs" say it is 13Ah.
Whether it is just a mistake or a deception, either one makes the seller untrustworthy and I would not purchase anything from them (because you cannot trust *anything* any of their pages say about any of their products).
Even if they were trustworthy, that battery is (as others have said) completely insufficient for EV motor use.
You would have to parallel 40 or 50 them to get any reasonable current out of them for a high powered bike like the Stealth series, and at that point you'd need a trailer to carry them.
I'd recommend checking out http://ebikes.ca
or maybe Luna or even Allcell, for ebike batteries.
But before you look into a battery, you first need to know what the current (amp, A) requirements are for the bike it's for. Then you have to see if the battery you are looking at can handle that.