| Word | Description |
| Fast Charge | A high rate charge — typically above 20 amps — for one to five hours that provides a quick blast of energy. It is often used to get the battery to a recharge level that can restart a vehicle. Repeated fast charges overcharge the battery and reduce service life. |
| Float Charge | A low, constant-current or constant-voltage charge that compensates for the self-discharge of a battery normally used in a standby application. |
| Flooded Battery | A type of liquid, lead-acid battery. See Vented Battery. |
| Frequency | The number of times that a periodic function, such as current or voltage, repeats the same sequence of values within a unit of time. It is measured in hertz. |
| Fuse | A safety device in a circuit that melts "open" at a specific level of current in order to protect the circuit from shorts circuits and current surges. |
| Fusible Link | A type of fuse in a circuit consisting of a reduced number of strands of wire held together by solder. |