Thanks for this guide! I discovered right away that I bought the battery for the 5548 accidentally and had to ship it back. I got the battery for the 5584, and by following this guide, I got it up and running within minutes.

One concern: the new battery has a closer port for the motherboard connector tab, which means the cable for that tab has to bend a bit. Hopefully I haven't introduced a problem with heat or anything.

My scroll wheel seemed clean enough. Everything except scrolling works, and I tried replacing the batteries as well. At this point, I'm assuming it is that light you mentioned not working, and I'm not sure what would be the issue: the light itself? The sensor (assuming the light is also infrared)? Part of the PCB?

But it was still neat to see the inside of the mouse. Thanks!