A while ago another member asked if they could use a button top battery in a pico. I have pico's and managed to fit an aw imr button top battery in one. It was difficult to do, had to really press down on the cap while turning but I got it in there and it worked. I was just testing it so I immediately took it back out, but it is doable.The battery will be fine. I have two batteries that are button top and they are a little longer than standard and the battery cap won't fit. The rest of mine fit fine. Those two that don't fit are really old. One is an old Efest (over rated at 35A) and the other is a black no-name with a silver generic sticker on it.
If you want to measure, the LG HG2 I'm using is 65.2mm long.