Car batteries provide the electrical energy to ignite the fuel/air mixture in an engine’s combustion chamber which in turn starts the engine and powers all the electrical components in the vehicle. That is the simple explanation, the bit we can all understand, but what about all the jargon and tech words we come across when trying to find the right classic car battery?
Rather than being a straightforward affair, choosing the correct battery can sometimes be confusing and could result in buying the wrong type – a battery totally unsuitable for the electrical demands of our classic car.
To help better understand battery terminology we have put together a jargon buster of words and terms below – some of which you will need to be familiar with when searching for a new battery for your classic car, others that will come in handy for caring and maintaining your vintage car battery.
One of the most overlooked upgrades is your classic car’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 does not 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.
How to Read and Understand Car Battery Specs Stickers—And How They Relate to The Real World.
Amperage Ratings
Every battery posts the amperage ratings on the top label. This tells you how much power the battery can provide.
- Cranking Amps (CA)– the rating of cranking amperage measured at 32 degrees F. CA is the discharge load in amperes that a new, fully charged battery at 32 degrees F can continuously deliver for 30 seconds while maintaining a terminal voltage equal to or higher than 1.20 volts/cell. CA ratings can be misleading because they can be up to 30 percent higher than the equivalent CCA rating. The BCI requires that a battery carrying a statement of its CA performance must also list its CCA capacity.
- 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. CCA is the discharge load in amperes that a new, fully charged battery can deliver at 0 degrees F for 30 seconds while maintaining a voltage of 1.20 volts/cell or higher. This measures the battery’s ability to start (crank) an engine under low-temperature conditions where the chemical reaction inside the battery slows down: A battery puts out 100 percent of its rated power at 80 degrees F, 65 percent at 32 degrees, and only 40 percent at 0 degrees. CCA is great for comparing battery performance in cold climate areas, but in hot climates lead-acid batteries with extremely high CCA ratings may have a shorter life than those with lower ratings: Within a given overall battery case (group) size, upping the CCA requires thinning out the internal plates to squeeze more out of them within the same case volume. Thinner plates are more susceptible to vibration and overheating.
- 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. RC is if listed, is the number of minutes a new, fully charged battery at 80 degrees F can be discharged at 25 amperes while maintaining a voltage of 1.75 volts/cell or higher. For a 12-volt battery (six cells), RC is the number of minutes it can maintain a voltage of 10.5 volts with a 25-amp draw; therefore, a “75-minute” battery lasts 75 minutes under these conditions. The bigger the RC, the better; modern cars with lots of accessories can see a current discharge rate much greater than 25 amps.
- 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. AH is a little tricky. Sometimes also known as the “C20” rating, usually you will see this on a deep-cycle battery sticker. It is a measurement of how much energy a battery can deliver continuously for 20 hours at 80 degrees F without falling below 10.5 volts. If a battery is rated at 100 amps/hour, it will supply 100 amp/hours of power, or 5 amps/1 hour. However, in the real-world total discharge time and load applied is not a linear relationship. As load increases, realized capacity decreases. This means if you discharged that same 100 amp/hr. battery by a 100-amp load, it would not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 amp-hours.
- Date Code:Most batteries have a date code, usually a long string of numbers and letters that show when the battery was purchased. One row of one- or two-letter codes indicates the month, the other row of numbers is the last digit of the year. The relevant date code in the ID should have been stamped or highlighted at the time of purchase.
- Group Size:This is the standard “envelope size” of the battery case that equates to its height, width, length, and terminal position, as established by BCI. Batteries with the same group number physically interchange. In many instances the group size forms at least part of the battery manufacturer’s part number.
The other side of the label tells you the type of battery and usually features a purchase date selection used for warranty purposes.
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 and do not become condensed. When installing a battery in the trunk, a firewall must be installed to protect the passengers; the battery box must also be vented to the exterior of the vehicle.
A typical flooded battery has caps on the top for the water. Some are one-time fill, others are serviceable.
- 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 do not 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 must 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 does not 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 cannot 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. 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. 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.
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 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 cannot 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, golf carts and show cars (lights and stereo systems). Deep cycle relates to the torture test that (assuming it passes) lets a battery truly call itself “deep cycle.” An SAE-specified measurement of the battery’s ability to withstand repeated discharge/recharge cycles, it lasts over 100 hours. The severe test offers the best overall gauge of automotive battery performance under severe operating conditions. Because of the test’s severity, you generally will not see this info published except for batteries specifically designed for “deep-cycle” service. Deep-cycle batteries are typically used on race cars without an alternator that require a between-rounds recharge, or in a streetcar that sits in a parking lot for hours with a high-amp stereo system on and the engine off.
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.
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 awfully expensive. A single lithium ion starting battery can cost over $1,500.
- NiMh – This design uses hydrogen-absorbing alloy as the negative electrode, and nickel hydride 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 batteries are remarkably like NiMh batteries, but they are slightly more efficient and hold a static charge for longer periods. These batteries are becoming more prevalent in 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 $1700. Using an Li battery in cold weather is not advisable though, as they can be damaged in temperatures below freezing.
Car battery specs conform to standards developed by the Battery Council International (BCI) and the SAE. Many of the specs appear on the common battery label or sticker as well as in battery manufacturers’ published literature. For car guys, the most important specs listed above give you the basics to understand car batteries, and what may be best for your classic car.
Great content, it will help in my business Thanks for sharing useful information. Respectfully, David, author of the blog https://agmbatteryguide.com/
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Awesome guide.
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