button top or flat top doesn't matter. As long as the bottom of the Kick can make contact with the top of the battery you're fine, and I have yet to encounter a flat top that couldn't. In certain mods where there is very little room for size variation (and taking into account the slight size variation from Kick to Kick and battery to battery) I guess you could potentially run into an issue with a particular combination not fitting, but I think this is a very rare scenario. The battery spring in most mods has enough room for compression to allow for the amount of variation you'd encounter