I still have the manual for my mouse. Model number 64321.
When this mouse was manufactured it used NiCad batteries which developed a memory much more than the newer batteries. The older NiCad batteries needed to be conditioned occasionally so Kensington provided a way to do that with the charging base.
The red light is for indicating discharge status of NiCad batteries.
The red light will flash quickly when you press the battery discharge button on the bottom of the base. This indicates that you now have 5 seconds to place the mouse in the charging base for battery discharge.
The red light will flash flash more slowly when the battery is being discharged.
After the battery is fully discharged, the base will then charge the batteries.
It should be noted that very few manufacturers of products that utilized NiCad batteries provided a "battery conditioning" feature. Kensington was unique in this regard. Battery conditioning allowed NiCad batteries to have a longer useful life.
Now maybe you can help me.... I lost my power supply that plugs into the USB connector. If you have yours, can you tell me what the output voltage is and what the polarity is of the inner pin. This will be marked right on the power supply base.
I plan to just get a generic power supply from Radio Shack, but I need the voltage value and polarity. Until then, I can still use the mouse, but it won't charge. FOr now, I'm just using standard AAA batteries.