Six lead-acid cells of about two volts each, wired in series. Its real job is one short, enormous burst of current — several hundred amps — to turn the starter; after that it mostly idles as a buffer. Start-stop cars use a tougher AGM or EFB version built for constant restarts.
A generator spun by the engine's belt. It actually produces three-phase alternating current, which a built-in diode bridge rectifies to DC and a regulator holds at about 14 volts — slightly above the battery's own voltage, which is what makes the charge flow into it.
A powerful DC motor that only runs for a second at a time. A solenoid throws its small pinion gear into the flywheel's ring gear and spins the engine fast enough to fire, then the pinion retracts so the running engine can't drive it back.
A single machine on the accessory belt that replaces the alternator and the starter. Driven as a motor it restarts the engine almost silently and adds a shove during acceleration; driven backwards by the engine it becomes a generator and recovers energy that braking would have wasted.
Hundreds of lithium cells grouped into modules inside a sealed, structural case in the floor. Wiring them in series is what produces 400 or 800 volts; wiring groups in parallel is what produces the capacity in kilowatt-hours. It is the heaviest single part of an electric car.
Battery management system
The pack's guardian. It measures the voltage and temperature of every cell group, balances them so none is over- or under-charged, calculates the state of charge you see on the dash, and limits current when the pack is too cold, too hot or nearly empty.
Turns the pack's direct current into the three-phase alternating current the motor needs, switching thousands of times a second to set the frequency — and therefore the speed and torque. It also runs in reverse during regenerative braking, converting the motor's output back into DC for the pack.
The bridge between the two worlds. It steps the pack's hundreds of volts down to about 14 volts to run the ordinary 12V network and keep its small battery charged. In a hybrid or EV this component does the alternator's old job, without any belt.
The rectifier the car carries with it. When you plug into an AC socket or wallbox, this unit converts the mains alternating current into the direct current the pack can absorb — and its rating, typically 7 to 22 kW, is the hard ceiling on how fast AC charging can ever go for that car.
More than a socket: alongside the power pins are signalling pins the car and the station use to agree on current, plus a latch that locks the plug and a temperature sensor. DC rapid charging uses extra, heavier pins that bypass the on-board charger completely.