The Battery Pack has four Light Emitting Diodes (LEDs) located above the WHOOP logo on the top (left side) of the device. (see image below)
Red/Green Charging LED
The topmost oval-shaped LED will remain off, unless attached to a plugged in USB charging cable. This LED will then illuminate to show the current charge status of the Battery Pack:
Solid Red = Charging
Solid Green = Fully Charged
Once the Battery Pack is fully charged, it should be able to also fully charge your WHOOP Strap.
NOTE: There is no indication of the specific charge level (%) of the Battery Pack; it is either charging or fully charged.
The other three circular lights on the Battery Pack replicate the same light patterns as the LEDs on the side of the WHOOP Strap.
As a result, these LEDs indicate the battery level of the WHOOP Strap and/or present indicate the pairing status of the Strap.
For a detailed description of all possible LED patterns, check out this article.
Once you slide the Battery Pack onto your Strap, the Battery Pack will briefly display the Strap's battery level via the three white/red circular LEDs. After a few seconds, these LEDs will turn off and remain off unless the Strap (and battery pack) is double tapped.
NOTE: A combination of red and white LEDs indicates the Strap needs to pair with your mobile device. Check out this section for help re-connecting your Strap to your mobile device.