If you open it up, the strip is actually a thin PCB glued to the underside of the top of the case. Mine was a little loose, pressing it down made things work a bit better. It does still get worse at tracking when the batteries start running down (a sign that they need replaced/charged!).

Even when it’s working well, its resolution is disappointingly low though. More like a mouse with a scroll wheel with fairly large detents than the trackpad-like scrolling I was expecting.