The optical mouse on our main desktop computer had recently been giving us trouble, so I set out to replace it. Previously, we had two desktop computers, but we consolidated them into one that my wife and I both use and my son uses for playing educational games. I had a wireless, optical that was just sitting around, so I decided to use that.
Originally, I had some rechargable NiMH batteries to use with the mouse, but those had been lying around uncharged for too long it seems and were now not able to be charged. I picked up some new, higher capacity batteries and charged them up to be used with the mouse.
I replaced the old alkaline batteries I was using for the freshly charged, NiMH batteries, replaced the mouse battery cover, and then...nothing. The mouse wouldn't come on. I thought perhaps I didn't wait long enough for the charger, so I put the batteries back in to it and let them cook overnight.
This morning, I put the batteries into the mouse and still nothing. So, I pulled out the trusty multimeter and checked them. Sure enough, they were putting out a great voltage (actually the batteries say they put out 1.25 V, but I was getting a full 1.5 V). So I popped them back into the mouse...Nada.
It was then that I noticed something strange about the battery case. There was a little tab that was preventing one of the battery's positive terminals from contacting one of the pads! I guess that I must have left batteries in the mouse long enough for the contact pad to bend too far away. I also noticed a similar problem on the other side, but a few bends with some pliers had the pads pushed a bit closer to batteries.
I popped the batteries back in and now everything was working great.