More than likely the Logitech bluetooth battery level won't show on the Apple Keyboard/Mouse preference panel since it is a non-Apple product, even if LCC is installed. But again, I don't have a non-Apple bluetooth wireless to make sure, though I have been tempted to buy one for the past year.
What I meant to say that at least for my non-bluetooth wireless mouse, my battery level will be displayed as a tiny indicator on the top right of the image of my mouse in the Logitech Control Center preference panel. I have about 75% remaining, but I'm not all too worried since I use it home. Even with the older Apple Wireless Keyboard I hardly ever check my battery level.