[Wresting]

I bought one of these USB 'kits' over a year ago to use on my laptop, running Windows XP. Apart from having to change the mouse batteries more frequently than I would have liked (low battery voltage causes 'sticky' operation), I had no problems with either the keyboard or mouse until a couple of days ago, when (a) the mouse started to cause the cursor to jump around randomly, and open programs - presumably with a spurious button press - and (b) the keyboard also started to misbehave, missing some key inputs and adding ones I hadn't pressed.
Because it had worked all right before, I took it back to Tesco, who exchanged it for a newer model (H38FE2): however, this one has exactly the same problems as the 'old' one.
Does anyone have any insight into this strange behaviour?