Battery-pack protection comes in two basic types: voltage protection and current protection. Voltage protection uses comparators to monitor individual cell voltages to see how they compare to thresholds that determine an overvoltage (OV) or undervoltage (UV) condition. As for current protection, a series sense resistor measures the current passing through the battery and compares it to predetermined overcurrent or undercurrent thresholds. This includes short-circuit conditions as well as levels for excessive charge or discharge. Most battery packs use MOSFET switches to control the charge and discharge paths; these also disable circuits if established thresholds are exceeded.