Change battery of Logitech Cordless Mouse

I have a keyboard and a wireless mouse from Logitech Cordless Desktop Express reference.It have Two AA batteries, I want to know that at what time intervals it is necessary to change the batteries? Can anybody advise me. Thanks in advance.

I contacted Logitech who advised me the following operations:
1 - Remove the batteries located inside the keyboard and mouse.
2 - Hold for fifteen seconds on the button "Connect" on the receiver.
3 - Wait 30 minutes and then replace the batteries inside the keyboard and mouse (preferably fresh batteries).
4 - Then press the button "Connect" on the receiver then press the "Connect" button located under the keyboard.
5 - Wait about twenty seconds.
6 - Press finally again on the button "Connect" and then on the receiver underneath the mouse.

To try to fix this, I ask you to follow these actions:
- Remove, as a first step, the batteries in your mouse.
- Using a metal object, touch the terminals of your mouse.
- Replace the batteries inside the mouse and then connect it to its receptor.

Once done, the problem you are experiencing should be corrected.

Recently, I have a wireless mouse with USB key. I just have to change the batteries mouse. I put my 2 rechargeable batteries and I want to have other opinions, if it's normal that it consumes as much. Yes of course you turn it off whenever possible if you let the pc function. But even less than two weeks, AA batteries long. On the other hand, the small indicator light on the USB key will work there a long time (there is no battery). Thank you.

Yes the small indicator on the USB key will work long, it the PC is powered by it.
Apart from that it is because of the consolation that I have no wireless mouse. It consumes a lot of these wireless mouse! The characteristic are:
- Wired mouse
- Rechargeable
- Mouse comprising a rechargeable battery that simply rest on its support. (Some models exist).

On the pack keyboard / mouse wireless for my mother (it's not Microsoft, but good) There's a button on the base and two buttons: one under the keyboard and one under the mouse. To align the frequency you have to press one of the base, press the keypad and then press one of the mouse. I hope it's the same with you.