Low mouse battery alert change and adjust

Is there something, probably a system prefs add on, that alerts a user on a Mac (Snow Leopard in my case, but also Lion) when an Apple bluetooth device (keyboard, mice) battery reaches a certain charge level?

I'd like to be alerted when my mice and keyboard Lithium/Lithium Ion/Li-ion/NiMh (wait, are those the same?) cells reach 50%. A little pop up window would do. Kind of like what the system does now but warning at 60% and final warning at 50%.

or is there a way to change that system alert so it does so at a 50% charge?

It looks like the system alert is not set for NiMh and would alert before actual 50% level though… bummer.

It would probably be a system pref add on to alert you accuratly of a low NiMh battery level in an apple bluetooth device.