Everything with a micro-processor does.. Even a tiny amount, its still measureable... And the problem is that beacuse its drawing current just keeping the internal electronics awake, it could keep going until the battery is totally flat (unless the battery can sence the total discharge and go into some kind of deep hibernation mode).
That said, I don't know what the draw is.. it could be so tiny (mico-amps) that it would take years to fully discharge.. But I just urge you to be careful leaving batteries in for extended periods of time, as there will be some electronics inside which will gradually draw current.
That said, the batteries have their own electronics which probably draw tiny current too.. Even even outside of the dock they will probably discharge over time...
So personally, I would leave them in the dock and get in the habbit of checking them.. And if the level seems low, give them a top up..