There's always going to be a little bit of a trickle discharge when it comes to any electronics, particularly more "intelligent" ones. For instance, the Wiimote, X360, and PS3 controllers all have circuitry that has to sense whether the user is holding the power button.
The problem is that, out of the three, the Wiimote seems to draw an unnecessarily large amount of power for that simple check. In my experience, I can keep batteries in my second Xbox 360 controller for months without an issue. If my Wiimote (well, back when it f'ing worked) had a set of batteries in it for a few months they would be nearly dead, if not completely dead.