An undervoltage warning is a lightning bolt icon that appears on your screen when there is insufficient power going into your pi-top.
The following checks can be made to resolve this:
- Ensure you're using a pi-top  Power Supply Unit that is connected directly into the mains power source.
- The lastest pi-top OS is installed on your microSD card.
- Try with a new SD card in case your existing SD card has become corrupted.
- The Cooling Bridge has the correct Thermal Pad affixed.
- The Cooling Bridge is connected properly to the Raspberry Pi pins and Hub