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Is a car's battery charged by the engine?

Can you tell me, if the battery is low on a journey can it be charged by the engine?

Jim Mctiernan (Sligo)

Oct 2020 Filed under: electric cars

Expert answer

Hi Jim,

If you're talking about a regular combustion-engined petrol or diesel car and their 12-volt battery, then yes, assuming the alternator is working properly, it will be driven by the engine and will charge up the battery so long as the electrical load from the battery is less than it can supply.

If you're referring to plug-in hybrids, and their high-voltage lithium-ion batteries, then it's not as simple as that and it differs per model and even depends on the driving mode. Most will, by default, use the battery to the fullest before starting up the engine and then may not charge the battery much except for kinetic energy recovered during braking. The idea is that you plug them in to charge up the battery regularly for maximum efficiency. However, most of them have a setting to override that and actively charge up the battery using the engine. It's usually activated by a button or option in the infotainment menu.

Shane O' Donoghue - Complete Car Advisor

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