Changing the batteries in a hp optical wireless mouse

I had this problem too. I couldn't figure out how to change the battery. On my HP Precision Laser Tracking mouse all you have to do is simply press on the button near the HP logo at the bottom of the mouse. It will open up the compartment where the battery is. Hope this helps.

From pictures, it looks like the top part of that mouse slide down.

Try holding it with the buttons facing toward you, and pushing with your thumbs on the top silver piece of the mouse away from you.

HP x4000 series.. mine has a moustache on it...
Pry off the top - as Andrea said, then there is a little plastic clip holding the batteries in. press the plastic tab forward, and the clip pops out. pry out the 2 AAs and reverse the process.

My HP Wireless mouse has NO compartment or door or button on the bottom, to open the mouse up! So I hunted along the top, and finally figured out how to open it! The TOP portion of the mouse, or the "lid" that sits on top of the main body of the mouse -- needs to be flipped off. However, it is NOT the upper end, where your fingertips click and scroll. It is the OPPOSITE end, or the LOWER END of the top portion - - where the PALM OF YOUR HAND sits. This end clicks off. It is secured in place by 2 tiny little magnets inside. Simply put your fingernail, or the sharp tip of a very thin knife, under the "lid" of the mouse, at the center point of the lower end, and it will click or pop right up! Ta-Da!! I kept on trying to force the upper end, where the clicker has an opening. It is a miracle it did not break!! I have now scratched a little arrow at that spot, so next time I will remember where to open! Good luck - - You CAN do this!!!