I dont think you would have a problem selling it at all - I have tow batteries for my bike, and would for any EMTB I own in the future, simply because you can keep one in the car, have a spare charged up ready to go if you are riding multiple days in a row, and many other reasons. The 700wh isn't enough of a battery to do a full day at some of the bigger trail centers, so even if I had a bike with a bigger battery I would still have a spare.
I also think there is a market for those with the bigger batteries in their bikes wanting the smaller barttery too, as it save a fair amount of weight. If I had an S-Works, I would want the smaller battery in it for most rides, and only use the bigger one for longer days.