Car Batteries 101 – Automotive Battery Guide For Any Driver
One of the most overlooked car parts is your vehicle’s battery. While the type of battery under the hood is not likely to give you any horsepower gains, it will save you from having to get jump started in the middle of the night at the gas station. Additionally, a properly functioning battery means your alternator doesn’t have to work as hard, and getting the best performance from your charging system is always good bet, especially if you have upgraded electronics. This automotive battery guide is here to help you on your next trip to pick up a battery. You will learn which one to grab and which ones to leave on the shelf.
- Cranking Amps (CA) – the rating of cranking amperage measured at 32 degrees F.
- Cold Cranking Amps (CCA) – the amperage rating the battery can provide at 0-degrees F for 30 seconds without dropping below 7.2 volts. This is the most important measure of a battery, and is the typical rating used for selecting the appropriate battery for a vehicle.
- Reserve Capacity (RC) – measured in minutes, this is how long the battery will provide 25 amps until the battery voltage drops to 10.5 volts. This is used on both starting and deep cycle batteries.
- Amp Hour (AH) – typically used for deep-cycle batteries, this illustrates the amperage capacity. A battery with 150 amp hours rating would provide 15 amps for 10 hours, 10 amps for 15 hours or 150 amps for 1 hour.
Common Battery Types
While most batteries are of the same age-old lead acid (LA) design, there are many ways to put them together. The main types are flooded, gel and AGM (Absorbed Glass Mat). All lead acid batteries use the same overall concept – lead plates (one is lead, the other is lead oxide) are submerged in an electrolyte solution of sulfuric acid. Each of these plate groups is called a cell; a group of individual cells is called a “battery”. As the battery discharges, the lead electrodes become lead sulfate, and the electrolyte dissolves into water. This why batteries freeze during the winter, which can cause the lead plates to touch (short-circuit), effectively destroying the battery. While charging a lead acid battery, through electrolysis, the battery generates oxygen and hydrogen gas, which can be explosive, which is why batteries are typically mounted under the hood, where they dissipate gases and do not become condensed. When installing a battery in the trunk or interior cabin, a barrier must be installed to protect the passengers. The battery box must also be vented to the exterior of the vehicle.
- Flooded – This is the most common type of LA battery but there are couple subgroups – conventional and sealed. Sealed flooded battery are designed to be maintenance—free, meaning you don’t have to add water at any time, they are sealed. Within a conventional battery, such as a “tar-top” battery in a classic car, each LA cell is separated and each group has its own electrolyte. Over time, the process of charging and discharging uses up the electrolyte and it has to be replaced with distilled water. Some modern batteries still require this kind of maintenance.
- Gel– The platform is the same, but instead of using plain old water as the base for the electrolyte, they use a thickened version (like Jell-O) to keep the electrolyte from leaking in the event of a cracked or broken box. This also makes the battery more stable in terms of vibration and installation location, as the gel doesn’t move, which ensures the plates are always covered in electrolyte. One of the drawbacks for gel cell batteries is that they are more susceptible to voltage irregularities and they can’t be refilled, once the electrolyte degrades, the battery is toast.
- AGM – AGM or Absorbed Glass Mat batteries are the most efficient of the lead-acid design. AGM batteries use a fiberglass separator to keep the electrolyte between the lead plates. This makes AGM style batteries extremely stable in any position, even upside down. NAPA offers an AGM type battery in the Legend series, which uses a flat-plate core with AGM electrolyte separators, making it impossible for the plates to touch. These batteries last much longer than a conventional or gel-cell battery, and are the superior design for wet-acid type vehicle batteries. AGM batteries also resist freezing longer than conventional batteries.
Both gel and AGM batteries de-gas like flooded batteries, but since they are sealed, the gasses are reabsorbed into the electrolyte, keeping them functional longer. Both types of batteries can release their charge faster than flooded batteries, which is an important function. In order to provide a larger level of cranking amperage, a flooded battery must be much larger, as a typical flooded battery is limited in how much charge it can release at one time. Gel and AGM batteries can release more charge at once. This means that gel cell and AGM batteries can fit in a smaller case while providing more amperage. They are very popular with off road enthusiasts and high-performance racing vehicles.
New Battery Types
There are a couple of newcomers to the automotive battery realm, specifically lithium Ion (Li) and Nickel-Metal Hydride (NiMh). These batteries are commonly used in rechargeable applications for cell phones and other portable devices, they are very stable and hold a charge for a long period of time, with the ability to release that charge quickly. Both types are very efficient and have a long life, but they are very expensive. A single lithium ion starting battery can cost over $1,500 while an electric vehicle battery can be several thousand dollars.
- NiMh – This design uses hydrogen-absorbing alloy as the negative electrode, and nickel oxyhydride as the positive side. NiMh batteries charge fast, but they have a faster discharge rate when idle. These are the type of batteries used in hybrid vehicles.
- Li – Lithium-ion batteries are very similar to NiMh batteries, but they are slightly more efficient and hold a static charge for longer periods. They are commonly used in fully electric vehicles like the Nissan LEAF, Ford Mach-E, and all Tesla models. They pack a lot of power in a small package with relatively light weight. These batteries are also attractive to high-performance applications where every pound is critical. Swapping a 40-pound LA battery for a 13-pound Li-ion unit has a definite advantage. In fact, Porsche recently swapped out conventional batteries for Lithium Ion, with a replacement cost of $1,700. Using an Li battery in cold weather is not advisable though, as they can be damaged in temperatures below freezing.
Battery Subclasses: Starting and Deep-Cycle
- Starting batteries – have higher cranking amps for heavy, short bursts of energy use a larger number of thinner plates to release more amperage. The thinner the plate, the more amps is can release in a burst. The side effect of this is that the plates get hotter faster, which causes them to warp and pit, particularly when they are fully discharged.
- Deep-cycle batteries – use fewer plates, but each plate is thicker, so they store more energy, but can’t release it as fast, only 25% of the rated amperage can be released at one burst. Deep cycle batteries are used for long-term constant draw situations, such as boats, RVs, golf carts and show cars (lights and stereo systems).
Flooded style deep-cycle batteries should not be used for starting; they do not have the cranking power. AGM deep-cycles can be successfully used as starting batteries.
Flooded batteries require more maintenance, but all batteries have needs. Lead acid batteries must be charged constantly to maintain that charge. Leaving a LA battery on the shelf for 6 months will degrade the battery, especially if it is in cold weather. You must protect your batteries from freezing. In severe cold weather a battery can freeze, which will short out the plates and the battery will no longer charge. When a battery freezes, the sides of the box will bulge.
- Charging – When storing a battery long term, you should consider a trickle or maintenance charger. These low-amp chargers keep the battery from discharging over time without boiling the electrolyte, which can ruin the battery. There is another side to that coin though. A dead flooded (this does not work for gel or AGM types) battery that won’t hold a charge can sometimes be “jump-started” by boiling the electrolyte with a heavy high-amperage charge. This is because over time and charge/discharge cycles, the electrolyte crystallizes (Sulfation) on the plates. Boiling the electrolyte can re-absorb those crystals, making the battery useful again. This does not work for batteries that have shorted cells. The process for reviving AGM batteries is a little more complex, involving multiple batteries chained together. AGM batteries need a better quality charger than a standard flooded battery, Optima Batteries offers an AGM-specific charger that doubles as a conditioner for long-term storage. Otherwise, a good, constant potential, voltage-regulated charger with the following rates- Charge / Absorption / Equalize between 13.8 – 14.6 volts @ 77°F (25°C), Float / Standby between 13.4 – 13.6 volts @ 77°F (25°C).
- Corrosion – Corrosion is a problem with all batteries, moisture, metal and electricity cause electrolysis, the same process at work inside the battery, but in an uncontrolled manner. That green fuzzy stuff on your battery terminals is bad. It is the by-product of electrolysis, which is like rust for lead. Preventing it is fairly simple and there are some methods that work better than others. You can buy the felt pads and anti-corrosion spray work, but not for very long. The key here is keeping moisture out while promoting a solid connection to the cables. A little Vaseline on the terminals goes a long way to protect against corrosion. Another solution is liquid electrical tape, which creates an airtight seal, but it has to be cut off before removing the battery cable.
- Water Level – Flooded batteries require water to function, over time, the water level decreases. While many flooded batteries are labeled “maintenance free”, not all are. You should periodically check the water level in your battery. If the water is below the top of the water holes, add some distilled water. You have to be careful, the water in the battery is highly-corrosive. AGM and Gel batteries do not require water maintenance.
- Cables and Terminals – The battery can only do its job when the connections are good. Corroded cables and terminals, loose fitting terminals, etc. limit the alternator’s ability to charge the battery and provide juice to the car. All terminals must fit tight, if you can wiggle it by hand, it’s not tight enough. You have to be careful with side-post terminals, as you can strip the threads and actually break into the case, causing electrolyte to leak out.
Battery Replacement Tips
When it comes time to replace your battery we have a few tips. For the exact steps to replace the battery in your own vehicle we suggest consulting a repair manual.
Regardless of the type of battery you choose, there will be some decision to be made. A daily-driven econobox doesn’t need a high-performance lithium-ion battery, while a show car needs a battery that can sustain long periods of use without charging. Find the right battery for your needs and it will serve up the juice you need for a long time.
Check out all of the batteries available on NAPAOnline or trust one of our 17,000 NAPA AutoCare Centers for routine maintenance and repairs. For more information on our automotive battery guide, chat with a knowledgeable expert at your local NAPA Auto Parts store.
Jefferson Bryant View All
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.
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