Rick's Free Auto Repair Advice

Start stop battery

Start stop battery

What types of batteries are used in start stop vehicles?

Start stop vehicles utilize either an enhanced flooded battery (EFB) or absorbed glass mat (AGM) battery. Both types provide more reserve power needed for start stop systems.

Enhanced flooded battery (EFB)

An enhanced flooded battery (EFB battery) is a variation of a traditional flooded lead-acid battery. It’s used in vehicles in start stop vehicles to improve starting and provide more standby power and to accommodate regenerative braking recharging.

EFB battery advantages over a starting lighting ignition (SLI) flooded lead-acid battery

• An EFB battery can provide up to 85,000 starts compared to only about 30,000 provided by flooded lead-acid batteries.

• An EFB battery provides up to 30% more cranking power than an SLI flooded lead-acid battery.

• An EFB battery doesn’t encounter the same acid stratification problems that affect SLI flooded lead acid batteries. EFB batteries contain tubes and passageways that allow the water/acid combination to remix during vehicle movement.

• An EFB battery allows for rapid discharge and recharge

Absorbed glass mat (AGM) battery

An absorbed glass mat (AGM) has positive and negative plates and separators just like regular SLI flooded lead-acid batteries. But instead of liquid electrolyte sloshing around between the plates, AGM batteries employ an absorbent glass mat between the plates to absorb and hold the liquid electrolyte. The glass mat is like a sponge that holds the electrolyte tightly against the plates. Because the electrolyte is held so closely to the plates, an AGM battery offers distinct advantages over an SLI battery.

Differences between an AGM battery and a standard lead-acid car battery

Each cell in an AGM battery is tightly packed so there’s more surface contact between the electrolyte and the plates. The high pack pressure reduces the internal resistance, reduces plate shedding, and increases battery life.

By design, an AGM battery off-gasses less than a typical flooded lead-acid battery. So it doesn’t have vent caps and it isn’t fully vented to the atmosphere. It’s referred to as a fully recombinant battery, which means it converts a larger portion of the gasses back into the electrolyte.

AGM batteries contain a valve-regulated vent that opens only when the internal pressure reaches approximately 3-7-psi. This pressure build occurs when an AGM battery is charged at too high a voltage or too high a current. The vent valve is a one-way check valve, so overcharging an AGM can cause permanent loss of electrolyte.

AGM batteries are NOT gel cells

Many people refer to cylindrical AGM batteries as gel cells. They are not. Gel cell batteries are never used in the automotive industry for starting applications.

Not all AGM batteries have cylindrical cells

AGM batteries can be made with flat plate technology or wound cylindrical cells.

What are the advantages of an AGM battery over an SLI or EFB battery?

An AGM car battery is designed to do three things better than a standard SLI battery:

• Deliver a powerful burst of power for starting the engine
• Run the vehicle’s electronics for longer periods when the engine isn’t running
• Last longer than either an EFB or SLI battery
• Provide less internal resistance

The glass mat and tight packing allow for easier electron flow during power demands and recharging. In addition, the internal plate chemistry and bus bars provide lower internal resistance which translates into more power from a smaller battery. In many cases, an AGM car battery will be smaller and deliver more power than a comparable flooded lead-acid SLI battery. An AGM battery provides up to 35% more cranking power than an SLI battery.

AGM batteries have a lower self-discharge rate

All lead-acid batteries self-discharge over time. AGM batteries have a lower self-discharge rate than SLI batteries, so you can leave them longer without starting the vehicle, and stores can leave them on the shelf longer without having to charge them.

An AGM battery is more resistant to sulfation and degradation

All car batteries are susceptible to sulfation, but AGM batteries don’t sulfate as easily as flooded SLI batteries. What causes battery sulfation?

AGM batteries lose less electrolyte

AGM batteries have an internal valve that regulates how much hydrogen gas is allowed to escape during charging. Batteries with these valves are referred to as valve-regulated, lead-acid batteries (VRLA). By limiting the amount of hydrogen and H2o lost, AGM batteries are more maintenance-free. You do not have to add water to an AGM battery

AGM batteries recharge faster than a SLI battery

Due to their lower internal resistance, AGM batteries recharge faster and at a lower voltage, which lowers the heat, which extends battery life. In fact, an AGM battery accepts a charge up to five times faster than a comparably sized SLI battery.

AGM batteries are more resistant to vibration

Because AGM batteries don’t have battery acid sloshing around and because the cells are tightly packed, they don’t shed as much plate material as SLI batteries.

Why do carmakers use an EFB battery instead of an AGM battery?

Enhanced flooded batteries are cheaper to build. They perform better than an SLI battery, but not as well as an AGM battery. If your vehicle was equipped with an EFB battery, you must replace it with an EFB battery. Installing a standard flooded lead-acid battery in a start stop vehicle will result in a much shorter battery life — as short as six months!

What happens if you use the wrong battery in a start stop vehicle?

EFB and AGM batteries are more expensive than SLI batteries, so owners are tempted to replace a bad EFB or AGM batter with an SLI battery. That’s a huge mistake. The charging systems in start stop vehicles assume you’ve used the correct battery and will charge the battery according to either an EFB or AGM charging protocol.

If you replace an EFB or AGM battery with an SLI battery, the charging system will destroy the battery within 6 months by overcharging it.

Do you have to reprogram a start stop vehicle when changing the battery?

Yes. As an EFB or AGM battery ages, the charging system adapts its recharging cycle to accommodate battery aging. If you replace the battery with the same type but don’t reprogram the vehicle’s computer, it will continue to recharge the battery at the same rate as the old battery, which will quickly destroy it. Reprogramming requires an advanced scan tool. Once the vehicle computer is reprogrammed it will adjust its recharging routine based on the fact that the battery is new.

©, 2021 Rick Muscoplat




Posted on by Rick Muscoplat


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