What is an AGM battery?
Your gas-powered vehicle requires a 12 V battery to run its electrical systems, including the starter and alternator, to get your engine going. The most important factor in choosing a battery is that it must meet your vehicle’s specifications. But even then, you have options. In this blog post, we’ll cover regular and AGM batteries and explain their differences.
Battery voltage
Volts are a measure of how much pressure goes through an electrical system. Think of water: you can stand in front of your garden hose at full power and probably enjoy the experience. But stand in front of a hose attached to a fire hydrant? Different story.
Voltage is the same, but with electricity. In technical terms, it measures the speed of electrons through a wire. All cars have a 12 V battery, even EVs. This battery powers your electrical systems.
Battery amperage
Measuring electricity requires different units of measurement. Amperage is another such unit. It measures how many electrons are flowing through a wire. The larger the amperage, the more electricity can flow through a wire. When a breaker in your home trips (automatically shuts off), the usual culprit is too many electrical devices and appliances drawing energy from that circuit. The automatic shut-off prevents the circuit from overheating.
What is a lead-acid battery?
Most lead-acid batteries today are encased in a sealed container to avoid electrolyte evaporation and dangerous spills. If you pop open your hood to inspect your battery, do not attempt to open it.
Why? Because the electrolyte is not an energy drink you ravenously ingest after a strong workout. It’s a mixture of distilled water and sulphuric acid, which can cause serious burns. Replacing the battery – so long as you follow some basic precautions – is safe. Opening it is not.
The interior of a lead-acid battery contains six connected cells, each one carrying about 2V. By comparison, an EV’s lithium-ion battery has 200-300 cells.
Lead-acid batteries fall into several categories, including AGM batteries.
How an AGM battery is built
Regular batteries use “flooded” technology. That is, the positive and negative plates needed to create the charge sit in a bath of electrolyte. This construction is sensitive to vibrations, and some evaporation is possible. Both situations reduce the lifespan of the battery.
An absorbed glass mat – or AGM – battery takes care of these concerns. Instead of being filled with an electrolyte, AGMs have the electrolyte infused into fibreglass mats. This means the electrolyte will not evaporate, and vibrations will not affect how the electrolyte engages with the plates.
AGM batteries and weather
The differences in construction between regular and AGM batteries also affect how your vehicle performs throughout the year.
Cold weather and 12V batteries
The differences in construction between regular and AGM batteries also affect how your vehicle performs throughout the year.
Off-season vehicles and AGM batteries
If you drive your vehicle only during warmer months and then store it over the winter, a flooded battery can sulphate if it’s not regularly charged. This means that the sulphuric acid in the electrolyte solution will harden, similar to how hard water leaves calcium deposits behind in your pipes, kettle, sink, etc.
However, unlike calcium deposits in your home, you can’t dissolve or remove the sulphuric acid deposits. Recharge it at least monthly to extend its lifespan.
AGM batteries, on the other hand, hold their charge much better. You should only need to fully charge your AGM battery once every three months when it’s not in use.
Which battery to buy: flooded or AGM batteries?
AGM batteries, because of their advanced technology, cost more. Some vehicles – usually older ones – may also require a conventional battery, but your owner’s manual will confirm this.
However, when you stand in front of a selection of batteries, including AGM batteries, you still need to weigh a few factors.
Factor #1: battery group size
Your owner’s manual will explain what size of battery you need. The group refers to the length, width, and height of a battery, as well as the location of the terminals. A battery’s group size must match the size of your vehicle’s battery compartment.
The Battery Council International standardizes battery group size. You can find their battery group size chart here.
Factor #2: cold cranking amps (CCA)
The CCA rating indicates a battery’s ability to start an engine in cold temperatures: how many amps can a battery deliver at 0°F (-18°C) for 30 seconds and maintain 7.2 volts? A battery with a high CCA rating is more likely to start a vehicle in cold weather. Choose a battery with a CCA rating that meets or exceeds the minimum requirement for your vehicle.
Factor #3: cranking amps (CA)
Similar to CCA, CA measures how many amps a battery can deliver for 30 seconds and maintain 7.2 volts.
Unlike CCA, though, this measurement is tested at 32°F (0°C). This measure can also be called hot or marine cranking amps.
Factor #4: reserve capacity (RC)
The RC rating of the battery indicates the battery’s ability to power a vehicle’s electrical systems if the charging system (alternator) fails. It measures how many minutes a battery can sustain at least 10.2 volts with the battery at 80°F (26.7°C) while discharging at a rate of 25 amps until the battery is drained. The higher the reserve capacity rating, the longer a battery can power a vehicle’s electrical systems.
Factor #5: vehicle use
Getting the “best” and “most powerful” battery may sound impressive, but if it outperforms your vehicle and driving habits, it’s a waste of money.
Consider how you use your vehicle when selecting a battery. If you often drive long distances or have a lot of electrical accessories, you may need an AGM battery with a higher CCA and RC rating.
AGM batteries in a nutshell
Absorbed glass mat batteries outperform flooded batteries in every criteria except price. They also typically last longer because they don’t evaporate electrolyte, are better protected from higher vibrations, and hold their charge better.
For more information on AGM batteries, or to book a car battery replacement service for your vehicle, contact your local NAPA AUTOPRO service centre and one of our friendly automotive technicians will be happy to help you.