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SLI 101 - The Basics

Power - by Joe Weber - updated on 6/29/2023

Different sized SLI batteries sitting in a garage

SLI, or Starting Lighting and Ignition, batteries are some of the most common batteries around. We use them every day, even when we don't think about it. They're in our cars, trucks, SUVs, RVs and more. Did you start your car this morning? You just used an SLI battery.

What Is An SLI Battery?

Starting, Lighting, and Ignition (SLI) batteries, are a type of rechargeable lead-acid battery used in automotive applications that are designed to provide a high initial burst of power. This is necessary for starting a car or truck's engine, as well as powering the lights and other electrical components in the vehicle.

How Does a Car and Truck Battery Work?

You insert your key into the ignition of your vehicle and turn the ignition or push the "Start Engine" button. Your engine starts and you're off to the store, to drop the kids off at school or heading into the office. How does that work? It's magic! No, it's really not, we promise. It's many years of science and engineering.

What really happens is when you turn the key, a signal is sent to the battery which then completes a chemical reaction to convert chemical energy inside the battery into electrical energy. That electrical energy is then sent to the vehicle's starter to spin the engine's flywheel to get the engine rotating. This allows the engine to suck in air and fuel. When combined with the spark from the spark plugs, the engine fires up and runs on its own. This whole process takes only seconds, which is an amazing feat of engineering.

If you'd like to dig deeper into how this happens, read our helpful blog "How Does a Car Battery Work?" and check out our handy video below!

Are There Different Types of SLI Batteries?


Chances are, if the vehicle is older, the battery in your car or truck is what is called a FLOODED battery. If you were to pick one of these up and move it around you would actually hear the electrolyte liquid sloshing around. The electrolyte mixture is just freely flowing throughout each cell. These batteries can potentially spill the electrolyte liquid if the case of the battery is damaged or is mounted on their side or upside down. These are your most cost-effective battery options.

An Enhanced Flooded Battery, or EFB is a step up from your traditional flooded lead-acid battery. These batteries are made with a poly fleece material lining each of the battery's plates, allowing for a more consistent flow of power. They are also built using thicker plates for a longer lifespan over traditional flooded batteries. Standard flooded batteries normally last between three and five years. EFB batteries can last up to six years or longer.

Many newer vehicles that have stop-start and other high-tech features use an Absorbed Glass Mat battery, or AGM battery. These are the next level of car battery technology. If you are looking for the best of the best that will provide stronger, longer-lasting power, this is your battery. AGM batteries are made with a fiberglass mat separator that absorbs the electrolyte solution making the battery spill-proof and allowing for more mounting positions. But not upside down. Not having any free-flowing liquid in the battery reduces the internal resistance which allows for more power production. AGM batteries also perform better in extreme climates than flooded batteries. Live in an area that gets below freezing often or over 100 degrees consistently? This is the battery for you.

Special Note

If your car or truck came with an EFB or an AGM battery, you should never downgrade to a traditional flooded battery. Doing so will cause problems with the operation of many electrical functions in the car. Always use what came with the car, or better.

How Do I Jump Start My Dead Battery?

Waking up to a dead battery is never a great start to your morning, and sadly, it's something that we've all had to encounter. Lithium jump starters are a great tool to have with you in case a dead battery happens when there is no one around with a car to use for a jump. They provide enough power to start your car in such a small package that you can keep it in your glove box. If you don't have a jump starter, which you should get if you don't, never leave the house without a set of jumper cables.

If you are using jumper cables:

  1. First, connect the RED positive clamp to the positive terminal of the dead battery first.
  2. Connect the other RED positive clamp to the positive terminal from the battery you are jumping from (the donor).
  3. Attach the BLACK negative clamp to the negative terminal of the donor battery.
  4. Connect the BLACK negative clamp to an unpainted piece of metal, or ground, on your car that is NOT the negative terminal of the dead battery.
  5. Start the working vehicle and let it run for a few minutes.
  6. After a few minutes, try to start your car.

What's the Best Way to Charge SLI Batteries?

In an ideal world, the alternator in your car or truck will charge the battery after every start while you drive. There's a lot of debate about how long you should drive in order to charge the battery. But, generally, a 30-minute drive would be sufficient to recharge your battery after a start.

But is that really true? There is a common thought out there that driving will recharge your battery back to 100%. Yes, driving at highway speeds, or at least keeping the RPMs over 1000 for an extended period, will recharge the battery to an extent, but the alternator also has other functions so it's not solely focusing on recharging the battery. So this is technically half-true. Yes, the battery will recharge but not all the way.

If you want to, or need to, recharge the battery all the way back to a full charge, then you should connect it to a maintainer.

What Is a Battery Maintainer?

A battery maintainer is essentially a battery charger, but smaller, that sends small amounts of voltage to your battery. Sometimes they are also referred to as "Trickle Chargers".

Connecting your battery to this type of charger allows the battery to come up to a full charge while simultaneously helping reduce the wear and tear it has been subjected to, which can make the battery last longer. These chargers are great if the battery sits for long periods of time without use and keeps the battery charged so it's ready to go when you need to use it.

Adding a battery maintainer to your garage is a great way to extend the life of your battery.

How Do I Maintain My Car's Battery?

Connecting your battery to a maintainer isn't the only thing you should be doing to ensure a healthy, long-lasting car or truck battery. All of these steps are absolutely doable, even for the newest do-it-yourselfer.

  1. Every now and then check to make sure that the battery terminals are clean and the connections are snug. If you see signs of corrosion you should immediately use the cleaner and brush in your Terminal Protection Kit to remove the corrosion.
  2. Use the terminal protection spray from your kit on the terminals and terminal clamps to prevent new build-up of corrosion. Install the terminal protectors from the kit on your battery terminals before reconnecting the clamps.
  3. Make sure that the fastener that holds the battery in place isn't loose or damaged. If the battery is moving around a lot while the car is in motion, it could get damaged.
  4. Routinely test the battery or have us test it for you to ensure that it is still reading the correct voltage, between 12.4V and 12.7V, and is not showing signs of failure.

How Does Temperature Affect Car Batteries?

If you go outside to work in the summer heat or the freezing winter, your body needs to work overtime to stay cool or warm while still working to the best of your ability. Your car's battery is no different and too needs to work extra hard in different climates.

Hot Weather

It's a common misconception that the freezing winter months are harder on your battery and shorten its life. In reality, the hot summer months pose a greater threat to your battery than the cold. Yes, the capacity of your battery may be higher in the warmer temperatures but the heat will also shorten the life of the battery. Here are three of the reasons why:

  • Overcharging
    Excessive use in high heat can cause the voltage regulator or other charging system components to malfunction which can lead to overcharging the battery. This is a good way to slowly kill your battery.
  • Evaporation
    Car engines get hot. Especially in the summer. Under the hood, after the engine has been running for a bit, the combination of the engine heat and the enclosed engine compartment can make a car battery reach internal temperatures of 140 degrees or higher. This can cause battery fluid to evaporate, which damages the battery's internal parts.
  • Corrosion
    High heat can cause the lead plates inside the battery to corrode and deteriorate. Resulting in a shortened life and reduced capacity.

All of these things can lead up to the battery becoming sulfated. The buildup of sulfation in a battery is something that you can't see from the outside and is quite problematic but can sometimes be reversed. To learn more about battery sulfation and how to correct it read our blog "What Is a Sulfated Battery?".

Cold Weather

The cold winter months are no better, especially when they follow that battery-killing summer. The cold weather affects batteries a little differently than the heat.

  • Reduced capacity
    Once the temperature outside reaches 32 degrees the capacity of the battery drops by about 20%. If you live in a state where it can get really cold, at -22 degrees it drops by 50%! This has a huge effect on the battery's ability to provide enough power to start the car.
  • Load increases
    The winter also brings with it shorter days which means you are going to be using your headlights more. You're also going to be using the heater, heated seats and more that you wouldn't normally use in the summer which will increase the power demands of the battery.
  • Reduced recharge rate
    Charging is slower in lower temperatures. When you start up your car on a cold morning and drive to work or school, the battery is not going to charge up like it normally does in warmer temperatures. Depending on the age of your battery and how cold it is, this could leave you stranded later on.
  • Thicker engine oil
    As it gets colder the oil in your engine becomes thicker. This is normal and is nothing to worry about per se but it can have a drastic effect on your battery. It will take more power to get the engine to turn over, making the battery work harder than usual.

What Can I Do to Prolong My Battery Life?

There is nothing you can do about the weather, but there are some things you can do to help keep your battery healthy and hopefully extend its life.

  • As we mentioned before, checking regularly for corrosion and removing any present is important to the life of the battery.
  • Using a battery maintainer during the winter will help keep the battery at a healthy charge.
  • Parking in a garage during the winter will help keep the battery at a closer to ideal temperature which may help reverse the effects of the cold on the capacity.
  • To help reduce the power demands of the battery, turn off and unplug any electronic accessories. And remember to turn off the headlights if you don't have automatic headlights.
  • While extremely rare, If you have a flooded battery in your car that requires maintenance make sure to check the fluid levels and top them off with distilled water if necessary.

Hopefully, by following these tips, you will be able to extend the life of your battery and, even better, not get stranded with a sudden dead battery.

Do Other Vehicles Use SLI Batteries?

Cars and trucks aren't the only vehicles that use SLI batteries. You'll find SLI batteries in cars and trucks, sure, but also in RVs, Boats, Motorcycles and other powersport vehicles.

RVs and Boats will often use more than one type of battery. An SLI battery to start the engine, and then a deep cycle battery that powers other electronic accessories that make the boat or RV whole. For help with choosing the best batteries for your boat or RV, check out our helpful Marine and RV battery buying guides.

Stop into your local Batteries Plus or shop our extensive SLI selection online today!

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