Energy recovery turns kinetic energy back into usable electricity, which is either stored in battery or used immediately.
During engine braking, the alternator voltage is higher than the battery voltage (maximum of 15V). The alternator then supplies the electricity to appliances and charges the battery. This saves fuel, which would be otherwise used on these tasks.
When the car is accelerating or driving steadily, the regulator voltage is lower than battery voltage (circa 12V), so the car uses the electricity stored in battery. The alternator works at lighter load in this mode, thus using less kinetic energy from the combustion engine’s crankshaft. The fuel supply is adjusted to the lower power use, which results in lower fuel consumption.
*Note: product images are for illustrative purposes only