Why do I need a special battery for the automatic start-stop system?

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Every starting process is associated with a large amount of energy from a car battery. The battery must be in a very good condition to reliably supply a high starting current. Especially with modern vehicles with automatic start-stop systems, the engine is switched off several times during the journey. During these phases the battery continues to supply all of the electrical consumers with energy. A conventional starter battery (SLI) is not designed for this charge output (i.e. continuous discharging and charging).

Only a battery with start-stop technology can deal with these demands and withstand the strain.

The generator charges the starter battery while driving

In a car which is not equipped with an automatic start-stop system, the starting process is usually a one-off event. While driving, the generator supplies the electrical consumers such as the entertainment system and navigation device, so that if the generator is working, there is no discharge of the starter battery during the journey.

The start-stop battery has a double load

The case is different for cars with start-stop technology. During a journey through the town, the battery is subjected to a series of start and stop periods. If the car is stationary at traffic lights with the engine stopped, electrical consumers such as lights, windshield wipers, radio or displays still need power. The load is increased by continuous discharge and charging.

In particular, short journeys present a challenge for the battery. Especially with old batteries and in winter, the charge acceptance of the battery reduces, so that adequate recharging during short journeys is not always ensured. This can result in gradual discharge of the battery, so that at some point, the battery no longer has enough energy to start the engine. Due to the special technology, the internal resistance of AGM batteries remains considerably lower than that of conventional batteries over their entire life, so that sufficient charge acceptance is also ensured over a long period and short journeys with many start-stop phases can be handled better by AGM batteries.

Three advantages of AGM batteries

Excellent cold-start characteristics

AGM batteries have a large cold start current. They powerfully start the starter motor and reduce its running time. Thanks to the cycle stability of AGM batteries the engine can be switched off and started again several times at short intervals, without the risk of difficulties when restarting.

Balanced state of charge

With modern vehicles, the AGM battery is not only charged by the generator, but is also fed by the braking energy recovery system. Normal starter batteries must be kept permanently fully charged and can therefore not absorb the energy which is generated by recuperation. AGM batteries can be operated in the partial charge range and therefore provide sufficient “extra” capacity to store the energy which is generated on braking.

High reserve capacity

The high reserve capacity ensures the power supply for all types of electrical components. The cycle stability of AGM technology ensures the power supply to components while also providing a high starting power. Even if the battery is not fully charged, because, for example, electronic assistants and consumers which ensure comfort are supplied during a stop, or the generator has been temporarily decoupled to reduce the load on the engine.

Interesting facts about start-stop technology

Start-stop systems require a battery with modern technology, because normal starter batteries are not designed to meet the higher demands of these vehicles.

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The architecture of the electrical system in modern vehicles requires a compatible battery technology in order to function properly and reliably. For this reason, in many vehicles, new batteries must be “registered” – the Battery Management System (BMS) must know what type of battery is installed in the vehicle in order to exploit its full potential. If an incorrect battery is installed in the vehicle or is not correctly registered, this can result in premature battery deterioration and another breakdown.

For this reason, only EFB or AGM batteries should be installed in vehicles with automatic stop-start systems. If an AGM battery is already installed in the vehicle, it must always be replaced with another AGM battery.

In an effort to reduce fuel consumption and comply with ever-tightening CAFÉ fuel economy and emissions standards, carmakers have integrated several new features in vehicles produced over the past decade or so. One such system is Auto Start-Stop, a system that shuts the engine off when the vehicle is in gear but at a complete stop.

It’s an effective design, but frequent shutdowns and restarts surely take their toll on the battery’s health, don’t they? And especially since the batteries required are enhanced flooded batteries (EFB) or absorbent glass mat (AGM), the replacement price is much higher than a standard lead-acid type. Keeping the battery in its best condition for as long as possible reduces cost of ownership, lowers the impact on the environment, and most of all, increases the owner’s trust in their vehicle.

Learn about how auto start-stop functions, how it affects the battery’s health, and ways to get the most battery life out of a battery.

How Auto Start-Stop Works

Governed by the vehicle’s engine control unit, the auto start-stop feature relies on input from various sensors and systems to determine when it operates and for how long. It must meet specific criteria such as a warmed-up engine, a fully-engaged brake pedal, a battery charge level at or above 70%, and other factors like the transmission’s status.

As the car comes to a full stop, the engine shuts off, typically for around 30 seconds to three minutes. During this time, the car’s accessory functions like the HVAC, radio, and heated seats are powered by the battery alone. Once the battery charge drops below a certain threshold, the vehicle restarts. It’s expected that a vehicle with auto start-stop performs between three and five times as many start cycles as a vehicle without it.

The Effect on the Car Battery

Since the highest strain a battery experiences tends to be the high demand of a start cycle, it stands to reason that failures are more frequent. That would be true with lead-acid batteries, but the EFB and AGM batteries that these vehicles are manufactured with are meant to withstand the added demand.

There are actually a couple of positive effects that a vehicle can experience. First, it prevents deep discharges since maintaining the battery’s charge level is a priority. As well, there are enhanced opportunities for charging the battery more efficiently during braking and deceleration if the vehicle has a form of regenerative braking.

However, the more prevalent effects are on the negative side.

• With exponentially more instances of the engine turning off and restarting, the number of discharge and recharge cycles are much higher, contributing to the normal wear and tear that shortens a battery’s lifespan.
• There’s higher starting load. With the increased workload the starter experiences, there’s more stress not only on the starter itself, but the more durable starter typically has higher needs from the battery.
• In extreme temperatures, both hot and cold, thermal changes due to the frequent cycles can impact battery health too.

Ways to Maximize Battery Life in Vehicles with Auto Start-Stop

Although AGM and EFB batteries aren’t that different in chemistry from traditional lead-acid batteries, the system itself warrants more diligent care and maintenance to ensure not just that it functions well, but so that the battery will last the four-to-five-year expectancy it should have, or even longer. Here are four ways to maximize battery life.

Keep the Battery Clean

Typically, a small sensor on the negative cable near the battery communicates the battery’s voltage to the computerized controller for the auto start-stop feature. If the connection is dirty or corroded, there’s an excellent chance that the system won’t operate as it should. Following routine battery maintenance using an acid-neutralizing terminal cleaner can aid in promoting a good connection, plus it’s vital for the charge cycle to replenish the battery.

Perform Regular Tests

Like all lead-acid and any other 12-volt batteries, EFB and AGM batteries for vehicles with auto start-stop should be tested routinely. Make it a practice that every vehicle that checks into the service department receives a battery test. Equipment on hand should be capable of testing all types of battery chemistries, so no special attention needs to be paid to whether the vehicle has auto start-stop technology integrated.

Ensure the Charging System is in Good Shape

Along with battery tests, routine checks of the charging system should be conducted. A weak alternator could be putting undue strain on the battery, preventing it from charging fully and reducing fuel efficiency since the vehicle won’t shut down as often at a stop – or at all. With the right testing tech on hand, a charging system check can be done at the same time as the battery test with virtually no difference in the time it takes to complete.

Use High-Quality Battery Replacements

Vehicle owners who either don’t care for the auto start-stop feature or who are more budget-conscious than others might be inclined to forego the costlier EFB and AGM battery replacement in favor of a cheaper lead-acid variety. Shops might offer these replacements without considering the effect on vehicle performance too. Even though the dimensions are the same, lower-quality batteries end up costing more in the long run with more frequent replacement intervals and more frustrating problems than if the correct battery was chosen initially. Only offer battery replacements that are compatible with the vehicle’s original features.

Encourage Regular Usage

Counter-intuitively, it’s actually beneficial to operate a vehicle on a regular basis. While keeping a vehicle’s mileage low and preventing wear and tear is often the reason for limiting usage, lack of use can affect battery health, and it’s true also for vehicles with auto start-stop. Driving at least once per week for 15 minutes or more ensures the battery is recharged fully, and it maintains the battery’s capacity to function its systems as intended.

Although they’re more durable than average, batteries for vehicles with auto start-stop require care to get the most lifespan out of them. These tips will help promote good battery health for your customers’ vehicles, keeping them satisfied and keeping you in control of their vehicle service.

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