While placed on a USB charger, the LED on your pen-grip mouse should respond as follows:
- The LED will flash rapidly for 30 seconds when it is first placed on the receiver.
- After this the flashing will continue, but at a slower rate for up to 90 minutes.
- Once the battery is fully charged, the LED will switch off.
So if the LED only flashes for a short time, this should mean that your battery was already close to fully charged.