The alternator (an AC generator) that the engine rotates also powers an AC-DC rectifier, which charges the battery while the engine is operating. There is no net discharge from the battery because it is continuously recharged while the engine is running and provides power for all necessary electrical functions, such as the ignition system and spark plugs, a virtually infinite number of microcontrollers, and small motors (seats, windows), to the infotainment and advanced driver-assistance systems (ADAS). The battery is charged by the alternator to match the load and can be “topped off” by charging the battery at a higher rate than load discharge.

What is unique about a stop/start car?

The start stop battery experiences several starts and stops times. The car’s other electrically-powered key functions, including lights, windshield wipers, radios, or displays, as well as the less-essential systems, like infotainment, still need electricity while the engine is off and the vehicle is stopped, as would be the case at a traffic signal. The battery must provide electricity while it is not being recharged, which presents a hurdle.

What’s the resulting impact?

It is obvious that during rides with several stops and starts, adequate battery recharging may not occur. The battery’s diminished capacity to receive a charge, particularly with old cells and over the winter, makes the situation worse. This may cause the battery to gradually deplete to the point where it eventually runs out of power and cannot start the engine again.

What traits do “standard” automobile batteries generally have?

The majority of modern cars use gel batteries, which are an improvement over “wet” batteries from the past. The former is a “closed” battery where any hydrogen generated (and representing water loss) by the battery gets recombined so that topping off is not required, whereas the latter periodically has to be “topped off” with distilled (mineral-free) water.

Both types have an electrolyte around the anodes. However, the addition of silica causes the electrolyte in the gel implementation to take the form of a gel rather than a liquid. When a battery is in an intact state following an accident or case crack (it happens), the user does not have to worry about fluid leaking out. This increases resistance to vibration of a vehicle, resistance against problems on inclines (think off-road vehicles), and eases handling and improves safety. Maintenance-free batteries are a common term used to describe gel batteries.

Does utilizing wet and gel batteries with stop/start provide any issues?

Gel batteries have a longer service life than traditional lead-acid batteries because of their reduced electrode wear. The gel batteries, however, are unable to deliver the high cold-start currents needed for stop/start within brief intervals due to their increased internal resistance. Their sensitivity to temperature changes and performance decline in colder weather is a second drawback.