I found that the cordless mouse that I had went through batteries at a hell of a rate. As I could see no real advantage that it had over a normal corded mouse I binned it and went back to a cheap corded one that actually cost less to buy than a packet of batteries would have for the cordless. I still have a wireless keyboard though but the batteries in that seem to be holding up really well.
There should be no problem just buying a mouse to go with your keyboard. I use different makes of keyboard and mouse and neither of them are the same make as the computer. If you decide to get another cordless mouse it should come with a USB plug in device to connect it with the computer independently of the keyboard.
me too harry,rechargeables in everything mate,i been using them from pondstretchers, a pack of 2 aa or aaa for 1.99,made by GP i think,they are good batteries,also Lidl when they have them are a pack of 4 aa or aaa for 2.99.they do save a fortune,especially in your cameras. [:T]