HOW TO REMOVE BATTERY COVER ON MOUSE

On the Magic Mouse 1 flip over the mouse to the back side and on the bottom you will see a black tab and push it down and the back cover will pop out and you will see the AA batteries. Take out the old AA batteries and before you insert the new AA batteries you must clean the contact points the (+) and the (-) on both battery slots. Use a q-tip or a soft rag to clean off the batteries residue so you will have a 100% contact and if you don't clean off the residue then it will not give you a 100% contact.

Magic Mouse 2 you can't remove the batteries and it is rechargeable only and its the newer version of the Apple magic mouse 1.

If you have the new Magic Mouse, it is rechargeable -- does not have a battery. Simply plug in the USB-power connecter in the slot on the bottom to charge it.