With most simple generic batteries there is a often a simple work around.
Recently someone had a folding bike acquired wanting a battery, a few pics , suggestions and a bit of simple diy and they had a working bike for little over £120.
Though the same style battery couldn't be found a suitable different type was found and easily retrofitted.
Same goes for a couple of freego owners, given a pic and one can recommend a course of action that doesn't cost mega bucks.
Generic type batteries are generally simple to give a recommend as long as the battery isn't integrated in the frame, other wise one is looking at a re-cell service.