Electric skateboards use regenerative braking, meaning the motors act as generators when slowing down and feed the recovered energy back into the battery pack. When the battery is fully charged, there’s no remaining capacity to accept this regenerated energy.
Braking with a full battery can push the voltage above safe limits, causing the system to disable regenerative braking to protect the battery. This can leave you with little or no braking power.
Daniel’s Recommendation: If you live atop a hill, a simple timer outlet provides an easy way to automatically stop charging before the battery reaches 100%.