What Is Taper (Gradual Slowdown)?

Taper (gradual slowdown) is the deliberate reduction of charging speed after the battery reaches a certain level of charge (often around 80%). This is not a fault or a device defect but normal behaviour that protects the battery: as the cells get closer to full, they cannot safely accept high current, so the vehicle's battery management system requests less current to reduce the risk of heating and wear. For this reason the first 80% charges quickly while the last 20% takes disproportionately longer; this difference is especially pronounced in DC fast charging. In practice the most efficient use is to stop fast charging at around 80% and continue on your way; completing to 100% can cause unnecessary time loss. This behaviour originates mainly from the vehicle, not from the charging device's brand; Bemis's DC fast-charging units also follow the current curve the battery requests. For example, on a long-journey break at a DC station, leaving the vehicle at 80% and continuing is far more efficient than waiting extra for the last 20%; when charging with AC overnight at home, since the time is already long, completing to 100% is not a problem. In other words, knowing about taper makes it easier to plan your time on the road.