Posted: 12/02/2022
Short for Starting, Light, and Ignition, SLI batteries are built to do one job well: fire up your engine. That big jolt of power needed to crank the engine comes from them. Once the car's running, they take a step back. Paired with a deep cycle battery most of the time, they’re part of a tag-team setup. The deep cycle one handles your power windows, headlights, and stereo. Made for quick, powerful bursts, SLI batteries aren’t built to supply power for long stretches. That’s exactly why they’re usually a little lighter and smaller than deep cycle batteries.
To understand how an SLI battery does its job, first, know what it's made of. Lead-acid batteries make up the SLI type, so inside, you’ll find six cells made with lead dioxide and lead. Acting as the electrolyte, a sulfuric acid solution fills these cells.
From the battery’s negative terminal to the positive one, electrons move the moment you turn the key in the ignition. Through the starter motor, that flow creates a current. Then the spark plugs fire and the engine starts. Without taking damage, the lead-acid cells push through this quick burst of current demand.
After the engine gets going, the alternator takes over and runs your vehicle's electrical system. That means the stereo, other accessories, and the lights. So the battery can do its job again later, the alternator also recharges it while you drive
Flooded lead-acid (FLA) batteries and sealed lead-acid (SLA) batteries make up the two main types of SLI batteries. The most common type found in vehicles is the FLA battery. Cheaper than SLA options, these need only a little maintenance. They also tend to leak more often and wear out faster. In most cars, the ignition system probably runs off a flooded lead-acid battery.
More expensive than FLA batteries, SLA versions need less upkeep and usually last longer. Because they’re sealed with pressure-release valves, SLA batteries are less prone to leaks compared to FLA ones.
Deep cycle batteries and SLI batteries each do a different job and come with their own set of traits. Built to give short bursts of high power, SLI batteries start engines and run electronics in gas, diesel, or other non-electric vehicles. They push out quick, strong currents and recharge fast. These aren't made for long, steady use or being drained all the way down.
Designed for long energy output over time, deep cycle batteries fit better in setups like solar systems, marine gear, and RVs. Deep cycle models handle low discharge levels without breaking down. They give off consistent power longer than SLI batteries do. You can run them down deeply and charge them back up over and over without killing them.
Unlike deep cycle ones, SLI batteries usually get recharged through a vehicle’s alternator. To fill up a deep cycle battery, though, you’ll need to hook it up to an external charger.
Choose an SLI battery that matches your specific type of vehicle—don’t just grab the first one on the shelf. Electrical needs vary from car to car, so the wrong battery might end up frying something you don’t want fried. Match the battery to your weather, too. In cold areas, a warm-climate battery might leave you stranded. In hot areas, one built for the cold might not last as long as you’d hope.
Start your vehicle regularly and drive it for at least 30 minutes; you’ll keep your battery charged that way. If your car sits for long periods, connect it to a battery charger every few months. That keeps it from dying on you at the worst time.
Leave your lights on too long or deal with a faulty alternator, and overcharging can become a problem. The battery’s lead-acid cells don’t respond well to that. Over time, it wears them out and cuts down the life of the battery.
Every few months, check the electrolyte levels in your battery. If those levels look low, add distilled water until they’re back where they should be.
A well-maintained SLI battery should give you several good years. Even a healthy one will still reach the end of its life eventually. Once that happens, recycle it instead of tossing it in the trash. Dumped in a landfill, these batteries leak harmful stuff into the ground... which nobody wants.
Arnold Motor Supply has been a leading supplier of auto parts since 1927. Founded and based in Iowa, we have auto parts stores all over the Midwest. Order auto parts online and you'll be notified via email once your purchase is ready for pickup at your local Arnold Motor Supply parts store.
