Microsoft wireless notebook optical mouse 1024`

Under the mouse where the usb stick fits.

I have a Microsoft wireless optical mouse 3000. There is a silver button on the end of the mouse that usually faces you when using the mouse. Press that silver button- while holding the button in, use your fingernail or something to help with gently lifting the main panel on the top part of the mouse. Lift up on the end of the panel that is closest to the silver button. The panel comes entirely off, revealing the inset battery. It took me a while to figure it out since I installed the first battery.. it has lasted over a year. Hope this helps with yours. Have a blessed day!