I discovered something for backpack layout that's not obvious, but logical. This became apparent on my PRO CRAFT backpack, the largest of three packs a own.
It's best to always store the batteries in the bottom of the pack (orientation while on your back). Many packs locate them in the top. This can make the pack top heavy, which doesn't feel as natural as having most of the weight in the bottom. This unnatural feel being top heavy is most apparent while carrying the pack temporarily for short distances using one strap over one shoulder. It just doesn't hang right. But after rearranging my three extra batteries to be in the bottom, it works much nicer on the back. Weight distribution matters.
You would assume that manufacturers of backpacks would realize weight distribution is important when it comes to hauling batteries. Apparently some didn't think about that.