I think the sliding battery is normal in the big one. I have one and it does that and works fine. By the way, it's pretty easy to get them apart. Just clamp it in a vice - gently - with the connector facing up. Don't clamp over the silver part, leave it sticking out the top. Don't squeeze the vice too hard or you could damage the battery - just tight enough so it doesn't fall out of the vice. Screw in an atomizer, preferably a dead one. slide in a dowel or metal tube. A tube is better because it will go in further because it will go down over the bridge. Rock the dowel/tube back and forth until the silver connector separates from the battery. It comes apart easily - no heat needed. I bet you'll find a burnt spot on the battery's circuit board. That's been the case on every one of mine that has failed.
