Stop start car battery, maintenance, types and charging

For close on a hundred years the car battery has had a relatively straightforward function: Store electrical power to drive the ignition system, the lights when required, and occasionally the starter. For the consumer this made battery selection very simple – Battery size (The Battery Council International assigns numbers and letters for each battery group size, referring to the battery size that best fits the physical dimensions as well as terminal configuration, for a specific vehicle packaging) and energy storage capacity was basically all that was required to successfully select the correct battery.

With the introduction of Micro Hybrid Electric (also known as Start-Stop) Vehicles this battery selection process became more complicated.

So while the traditional types of car batteries have been covered in a previous article we’ll take a closer look at batteries used in stop-start vehicles, before giving some general advice on selecting the best battery for the application.

stop-start exide battery

| What makes the Stop-Start battery different?

Stop-Start technology reduces exhaust gas emissions and fuel consumption by automatically switching off the engine every time the vehicle comes to a stop. However, cars fitted with Start-Stop systems also place a greater load on the battery.

Unlike in conventional vehicles, where the battery only has to provide a large current to turn the starter motor at the beginning of a trip, the Start-Stop battery has to cope with numerous discharge and recharge cycles over the course of a city drive. Moreover, while the engine is switched off, the battery has to continue powering the ancillary systems such as lights, air conditioning and in-car infotainment.

Unlike in conventional vehicles, where the battery only has to provide a large current to turn the starter motor at the beginning of a trip, the Start-Stop battery has to cope with numerous discharge and recharge cycles over the course of a city drive. Moreover, while the engine is switched off, the battery has to continue powering the ancillary systems such as lights, air conditioning and in-car infotainment.

As discussed in the article on “Car Battery Life and Maintenance” the Lead Acid Battery operates in a relatively narrow State of Charge window where, if the battery is discharged below its design limits, or deep-cycled, sulfation speeds-up which reduces the battery’s ability to accept a charge, resulting in a reduced lifecycle.

To cope with these demands manufacturers have developed technologies that ensure cyclability and deep-draw while safeguarding durability.

Read More

| Types of Stop-Start Batteries

Always mindful of the delicate balance between cost and performance, battery suppliers offer consumers two basic types of stop-start technologies:

ECM/AFB Battery

Catering for entry level start stop vehicles ECM (Enhanced Cyclic Mat), also known as Advanced Flooded Battery (AFB), has been specifically developed to provide increased performance, longer battery life and the ability to cope with additional cyclic demands at a lower cost than the alternative AGM (Absorbent Glass Mat) batteries.

Cyclability is significantly improved by increasing the electrolyte reservoir, while advances in the construction of the negative grids, which typically incorporate alloy of Lead, Calcium and Tin, results in longer service life and reduced water loss. The blend of expanders is also adapted to deal with the increase in number of cycles. In addition, by introducing a double layer separation the battery’s performance is optimized for the most demanding applications.

AGM Battery

AGM batteries are designed specifically for larger, more sophisticated stop-start vehicles that use additional energy saving systems such as brake regeneration and energy management to reduce fuel consumption. AGM batteries also cost a little more!

However, the AGM can charge up to five times faster than the normal flooded version, and has the ability to deep cycle, offering a depth-of-discharge of 80 percent, compared to the flooded that is specified at 50 percent to achieve the same cycle life.

AGM batteries also have a very low internal resistance, are capable of delivering high currents while promising an acceptable service life, even when deep cycled. The technology is maintenance free, provides excellent reliability and is lighter than flooded lead acid equivalents. These batteries also fair well in low temperatures while offering a low self-discharge rate.

| Selecting the right battery for your stop-start vehicle

While the above explanations describes why Start-Stop vehicle owners would have to fit either the AGM or ECB/ AFB type of battery, the question remains: “How does one select a battery that meets the performance and lifespan requirements without paying for functionality that is not required?”

This is a question that pertains to all Lead Acid Batteries, not only in special case Stop-Start applications.

The rule of thumb is quite simple:

Keep to the type and specification of battery that the car manufacturer specified for the vehicle.

This refers to the size, configuration, rating and technology/ chemistry. The car manufacturer would have selected a battery that is suitable for the performance and technical characteristics of the car, so when replacing the battery, it is best to stick with the same battery the car was designed with.

There are a limited number of very special cases where due to novel operating conditions, an operator may wish to upgrade the battery to reduce maintenance or extend the lifetime.

On the other hand, should a vehicle be required to operate under a wide range of climatic conditions, particularly colder temperatures, the AGM battery could be considered as a very capable, although costly, alternative.

| Charging a Stop-Start Battery

When charging an AGM battery, it is important to know they do not handle overcharging well. They can accept charge rates of about 2.40V/cell, with a float charge not exceeding between 2.25 and 2.30V/cell.

Car Charging System

During normal use your car battery will be charged by your cars charging system. For cars designed for flooded lead acid they normally have a fixed float voltage setting of 14.40V (2.40V/cell), which means that a direct replacement with a stop start battery could overcharge the battery on a long drive, reducing the lifespan quite significantly. This is one of the reason to stick with the battery the car was designed for.

Stop-Start Battery Charger

The AGM batteries sensitivity to overcharging must also be taken into consideration when recharging using a stand-alone charger. A car battery charger should be selected that has a mode switch for ‘AGM type batteries’ which limits the current to 20 percent of battery capacity at a charging voltage in the range of 2.4 volts to 2.465 volts per cell at 25°C/77°F.

You can buy chargers designed specifically for stop start batteries.

Temperature Compensation

When charging a stop start battery it is important to compensate for battery temperature by adjusting the charge and float voltages. The chemical process in the battery increase with higher temperatures and decrease with lower temperatures. The voltage of the charger needs to be adjusted to compensate for this change in the chemical process.

You will need to subtract 0.03V for each 1°C above 25°C or add 0.03V per cell for each 1°C below 25°C. Charging should be paused if the battery or ambient temperature exceeds 50°C. These figures apply to the total battery voltage and based on a 12V car battery.

It is not feasibly possible to know what the battery temperature is, so it is best to put the battery in the area that it will be charged for a few hours before charge to allow the battery temperature to stabilise with the air temperature.

Some car battery charges will automatically compensate for the temperature, so check the options you have available with your charger.

 

charger for stop_start batteries
Car Battery Monitor
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Car Battery Monitor

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| How to test a stop start car battery

Stop start car batteries can be tested in the same way as a standard car battery. You can use a multimeter or a Car Battery Monitor, both are inexpensive and easy to use.

Read more on testing a car battery:

| Summary

While this article provides the reader with a guide to cost effectively selecting a battery for a specific application, it is important that a ‘lesser’ battery, with regards to capacity, technology or performance never be used as a substitute – there might be an upfront saving but the downstream costs and consequences are not worth it.

 

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