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by Huw Evans  More from Author

Get Cranking With Our Battery Guide

Text by Huw Evans, Photography by Huw Evans and Johnson Controls

Most of the time your battery doesn’t warrant a second thought. That is, until one day, you try to start the car and…nothing. At that point it becomes almost as crucial as the tires. With the right battery and one that’s in proper working order, the car can be a joy, without it, well, let’s just say that a pain in the backside is more appropriate.

Although the battery is faced with the seemingly simple task of generating enough current to ignite a spark to start the engine, depending on the vehicle, driving and ambient conditions, as well as the condition of the battery, the ability to do that task and do it well varies tremendously. In this article we take a look at the humble automotive battery, how it works, how it has developed over the last five decades (since most of our Mustangs and collectible Fords were built) and what you can do to prolong battery life in your car, as well as save a bit of money.

In essence, automotive batteries are electrical storage devices. They employ a combination of an electrolyte (usually consisting of a solution of approximately 35 percent sulphuric acid and 65 percent water) along with lead plates or grids, housed in cells mounted in series. The combination of the acid and these lead plates creates a reversible chemical reaction and allows a great deal of energy to be stored within a very small space. It also makes lead/acid batteries rather heavy. The reversible reaction created by contact between the lead plates and the electrolyte generates electrical energy from chemical energy and vice versa. The electrical energy generated is discharged to the car’s ignition system to fire the engine. Once the car is running, the alternator controls the electrical current and restores electrical energy within the battery; ready for the next time it needs to discharge this energy to start the vehicle.

Automotive batteries usually come in two different forms, starter and deep-cycle. Starter batteries are those most often found in daily driven vehicles. These feature lots of very thin lead plates bathed in the electrolyte that forms individual cells within the battery. The plates in these cells allow for very intense bursts of electrical energy to be discharged at very short intervals, ideal for starting an internal combustion engine. However, deep or prolonged discharging can damage these fragile plates, causing them to collapse, preventing the battery from holding a charge and rendering it useless.

You’ll often hear this term; which is usually applied to heavy duty or more specialized batteries, particularly for industrial and marine applications. As the name suggests, deep-cycle batteries are designed for more demanding electrical systems; that require a more sustained electrical charge. Deep-cycle batteries feature thicker lead plates than starter batteries and dissipate a slower rate of electrical discharge. The thicker plates mean they can withstand prolonged and a greater number of discharges, more concurrent with heavy-duty use.

You can also find dual-purpose batteries, which are designed to promote quick starting as well as tolerate deeper discharges than standard starter batteries and are quite popular for modern automotive applications, because they not only provide a quick burst of energy for cranking an engine, but are able to sustain greater discharge periods and can support powerful stereos and an array of modern comfort and convenience options. However, because these dual-purpose units feature, thinner plates than pure deep-cycle batteries, they are a compromised design and won’t tolerate multiple deep discharges. Quite a few dual-purpose batteries are found in Marine applications.

When it comes to energy storage, how well energy is converted from chemical, to electrical and back again is crucial to battery operation and longevity. Known as energy conversion and calculated using percentages, it denotes the amount of energy that’s converted to heat and the speed at which the battery can be charged before overheating. The higher the percentage, the lower the internal resistance in the battery and better its conversion efficiency. Lead/acid batteries have a conversion efficiency of around 80 percent, versus 65 percent for Nickel/Cadmium or Alkaline batteries, commonly found in many household items.

Traditional automotive lead/acid batteries were flooded batteries with the cells molded into the top or bottom of the casing. Over time and use, the electrolyte would evaporate and could be replenished via small holes on the top of the battery. However, because the lead plates or grids were only supported at the top or the bottom, they were fairly susceptible to failure. In addition, these types of batteries had a fairly high Peukert’s exponent (see sidebar), meaning that high discharge rates and heat would drastically shorten their life expectancy. On many older cars, it was rare that one of these lead/acid batteries would last more than a year. Today you can still purchase these traditional style batteries, though they are expensive (often $200 or more) and best suited for trailer driven concours cars. If you plan on driving your Mustang or Ford, then you need to look at some newer and more reliable alternatives.

Today, most automotive batteries are VRLA (Valve Regulated Lead Acid) or AGM (Absorbed Glass Mat) maintenance free units. VLRA batteries use less electrolyte than flooded-cell batteries and feature positive lead plates that evolve oxygen, which combined with the hydrogen evolved from the negative side plates, creates water, thereby reducing the vaporization of water, common over time with traditional flooded cells. As a result, because the electrolyte cannot be topped, they feature casings that cannot be opened, though a valve vent is present to allow gassing should the battery be overcharged. AGM batteries are a further development that use a fiberglass type separator that’s bonded to the lead plates and casing. Besides keeping the electrolyte in place, it also makes for a spill-proof casing. Popular examples of AGM automotive batteries are those offered from Optima, which have gained widespread acceptance among car enthusiasts and motorsport communities. Because AGM batteries have lower Peukert’s exponents than flooded cells, they can dispense electrical charges at a much greater rate, have a much greater efficiency rate, and convert less than 5 percent of their energy into heat (versus a staggering 20 percent for traditional flooded cell-type batteries). This means that a smaller capacity battery can be used relative to higher electrical demands. In addition AGM batteries are incredibly tough, with a very high vibration resistance, one reason why you see a lot of them in aviation, military, and motorsport applications.

Because lead/acid batteries are so heavy, they can have a substantial effect on your car’s weight distribution. In many forms of motorsports, racers try to take as much weight off the front of the car as possible, to aid in weight transfer and improve handling. As a result, many drag and road race cars often have their batteries relocated to the trunk. A number of companies supply kits, which allow relocation of the battery using an extension for the positive and negative cables, often routed through the firewall and along the floor. Relocating the battery from the engine bay also cuts its exposure to heat down considerably which helps extend operating life.


Although we’ve touched on some of the principles relating to automotive batteries and how they work, nothing beats getting tips from an expert. As a result Mustang & Ford spoke with Daryl Brockman, an application engineer with Optima Batteries. Daryl explained some common misconceptions regarding battery use and maintenance, how different batteries suit different applications and why AGM units, like those offered from Optima have become increasingly popular in recent years.

Q: What are some of myths versus facts when it comes to battery maintenance, specifically gel or AGM units?

A: Although an AGM battery is truly maintenance free, that doesn’t mean that care doesn’t need to be taken when storing a battery, especially if it is connected to your vehicle at the time. Although an Optima battery has a lower self discharge rate (holds voltage) than most other batteries on the market, clocks, alarms and other "key off" loads can discharge any battery given enough time. Starting your vehicle for short durations a couple of times a week during storage can actually be worse for the battery than letting it sit. Unless you actually take the vehicle for an extended drive at highway speeds for a decent amount of time, the energy it takes to start the car may exceed the energy you are putting back in. Using a good, microprocessor controlled battery charger/maintainer when not using your vehicle will minimize sulfation (the creation of lead sulfate crystals), which can reduce storage capacity and shorten life dramatically. You can often see sulfation around the terminals on older or well-used batteries.

Q: Are modern batteries truly maintenance free?

A: All batteries will emit some gasses during normal use. A typical flooded-cell or “wet” battery will vent these gasses outside the battery. Because a consumer cannot add water to a typical maintenance free battery, eventually the battery can dry out.
An Optima battery is a valve-regulated design; under normal use the gasses are kept inside the battery and recombined actually making for a truly maintenance-free design.

Q: What is a battery’s worst enemy?

A: Other than not maintaining the charge of a battery in storage, the next biggest enemy is high heat. Many people believe that cold weather destroys batteries. Although extreme cold will test the power output, it doesn’t necessarily harm the battery. High heat can both reduce the life of a battery and increase the rate that the battery loses voltage when in storage. In addition to the United States military’s testing and use, numerous desert fleet tests have proven the superior performance of AGM batteries like those from Optima in extremely hot environments.

Q: How often should you replace your battery if you have a weekend driven classic or collectible car?

A: It depends on how the battery is used and cared for. I received an e-mail from a gentleman with a DeTomaso Pantera a few weeks ago, his Optima RedTop battery finally needed to be replaced after 14 years. His vehicle was exceptionally well maintained, there had been some upgrades to improve the efficiency of the electrical system, and he used a maintenance charger. Probably the single biggest factor in how long a battery will last in a non-daily driven car is how well the voltage of the battery is maintained while the vehicle isn’t being driven.

Q: Batteries used in different vehicles have different needs. For example tell us the different requirements being used in your street driven Mustang versus a drag race car?

A: An OE designs the electrical/alternator system to properly maintain all of your vehicle electrical loads and have a little extra to keep the battery charged. So the battery in the typical daily driver isn’t doing much more than starting the car, then the alternator charges the battery back up soon afterwards.

A drag race car is a totally different situation. Depending on what class you’re running, many don’t even have an alternator. Even in those drag race cars that do have alternators, what many people do not realize is that an alternator does not put out its peak amperage rating all of the time. So even if you have an alternator, it is only putting out its peak output for those few seconds when you’re making your run. From the time you leave the pits to the time the water pumps and cooling fans shut off after you make your run, the battery is being discharged. If you use a starting battery in this application it will have a shortened life. That’s where units like the Optima YellowTop come in. This is a dual- purpose starting and deep cycle battery. In addition to having great starting power, it can be deeply discharged many times and will be much more tolerant of this type of use.

Q: When did Optima batteries come into existence?

A: The original concept of a spiral wound AGM battery was developed for the United States Space program and powered the Lunar Rover in 1969. That technology was later purchased by Gates Rubber; which formed Gates Energy Products in 1972. The Optima brand was first introduced by Gates during the mid-’80s. Gates sold Optima in 1994 to Gylling, who in turn sold it to Johnson Controls in 2001. Johnson Controls is the leading supplier of lead acid vehicle batteries in addition to the leading independent supplier of hybrid battery solutions.

Q: How did the company identify a gap in the market for severe use/performance batteries?

A: Actually, the performance and enthusiast market found Optima. Early in Optima’s history, nearly all sales were to the military. Eventually Optima batteries started getting used in enthusiast’s vehicles and requests started coming in. The same characteristics that won Optima those early military contracts were also desirable to enthusiasts – long life, exceptional vibration resistance, non-spillable, long storage life, and high cranking power.

Q: From what we understand; Optima identifies different uses for its batteries via the color of the battery top – explain to us a little bit about that?

A: RedTop batteries are starting batteries, and are recommended for vehicles with stock or average electrical needs.
YellowTop batteries are dual-purpose deep cycle and starting batteries, and are recommended for vehicles with higher than average electrical requirements. If you have an audio system with amps, electric fans or water pumps, drag race car, air bag suspensions, etc, a YellowTop is the battery for you.

BlueTop batteries are what we sell to the marine and RV market, and they are internally the same as their RedTop or YellowTop counterparts. The difference is that BlueTop batteries have both automotive type posts, in addition to male threaded studs commonly used in boats and RVs.

This is used to measure the time it takes for a battery to completely discharge (originally at a current of 1 ampere) and is based on a formula devised by German scientist W. Peukert in 1897. For most lead/acid batteries, this is calculated using the formula:

T= C/(I/(C/R))n x (R/C)

T (stands for time, in hours)
C (stands for the capacity of the battery)
I (is the discharge current)
N (is Peurkert’s exponent)
R (is the battery’s hourly rating)

So if we use a battery with 100 amp capacity at a discharge current of 5 amps to find out how long it will take the battery to completely discharge, we can do the following:

T = 100/(5/(100/20))n x (20/100)
T= 100/ (5/5)n x (0.2)
T= 100/1 x (0.2) = 100 x 0.2 = 20

The time it will take for the battery to completely discharge is 20 hours. Using the formula, provided you have the correct hour rating, you can calculate the amount of discharge time depending on the current. So if we double the current discharge to 10 amperes, it should roughly take half the time the battery takes to completely discharge, compared with 5 amperes, so:

T= 100/(10/(100/20))n x (20/100)
T= 100/(10/5))n x 0.2
T=100/(2)n x 0.2
T= 100/2.46 x 0.2 = 8.1

So with a discharge current of 10 amps, our 100 amp capacity battery will be fully discharged in just over 8 hours, versus 20 hours at a rate of 5 amps However, the calculation can only work if the correct hour rating is used, otherwise it doesn’t work.

Based on these calculations you can see that using Peukert’s, the lower the discharge rate, the longer the battery’s run time (i.e. the time it takes before being fully discharged).

Today, reproduction, traditional flooded cell batteries are available, but they are fairly expensive and because they employ old technology, no more reliable than yesteryear. In most cases they are strictly for concours restorations.

Most traditional starter batteries are designed to discharge a high output of energy in a very short amount of time in order to fire the engine. Extended discharging really shortens the life expectancy of batteries like this.

On Ford Motor Company cars from the mid-’80s, like this Fox chassis Mercury Cougar, more modern Valve Regulated Lead Acid (VRLA) batteries are the way to go. This car has recently emerged from storage, which is often a good time to check a vehicle’s charging system and battery. Starting your car while in storage every week or so is harder on the battery than letting it sit for a few months.

Here’s a typical modern day aftermarket VRLA battery, in this case an Exide unit mounted in a 1991 Mustang LX 5.0. Because the fusion from the positive and negative lead plates creates water, there’s no need to top the electrolyte, one reason why these batteries have casings that can’t be opened.

The latest VRLA original equipment (OE) batteries, like this Motorcraft Max, are designed to withstand longer discharge periods, due to the greater array of electronic equipment contained within modern cars like this 2005 Mustang GT. This one has a three-year warranty, something unfathomable when the first Mustangs were built.

Because of the lead plates or grids and the electrolyte, car batteries are heavy to say the least. Many racers, in an attempt to improve weight transfer and or handling, relocate the battery to the trunk, as is the case with this Fox Mustang drag car.

Moving the battery to the trunk requires a new wire for the positive terminal and a new placement for the ground wire. In drag racing, many batteries are mounted close to the right rear wheel to provide good weight transfer and maximum traction at launch.

Here we can see the revised ground wire location in this Mustang. Many drag cars don’t use alternators, but require electric fans for cooling. This puts additional strain on the battery, one reason why dual starter/deep-cycle batteries are popular with racers.

The newest type of automotive batteries are so-called AGM or Absorbed Glass Mat units. These feature a fiberglass type material bonded to the casing and lead plates. Some of the most popular automotive AGM batteries are those from Optima. This is a cutaway sample of an Optima RedTop battery (note the circular cells). Because of their construction, AGM batteries like this are spill proof and a lot stronger than other VRLA or traditional flooded-cell batteries.

With the top removed, you can see the inside of this Optima battery. Notice how the lead plates are mounted in a circular fashion inside each cell.

Optima designs its batteries for longevity, high cranking power, spill and vibration resistance. RedTop batteries like this have been proven to last a long time, more than a decade in many cases – double the life span of many other VRLA batteries. This photo illustrates a sample cutaway inside one of the battery’s cells, showing a cross section of the absorbed glass matting and lead plates. Even though the cells and plates are designed to last longer in batteries like this, maintaining the voltage and combating heat is crucial to successful operation over time.

With more and more enthusiasts actually wanting to drive their classic Mustangs and Fords, a solid, reliable battery is more important than ever. A good VRLA heavy-duty battery is an ideal choice for cars like this ’68 Shelby GT 350, which is regularly driven (note the radial tires).

On an exotic or ultra high performance car like this Ford GT, an AGM battery is ideally suited, given the levels of power, heat and vibration generated from such. This car sports an Optima RedTop, which should provide reliable service for years.


If you own a classic cruiser or vintage Mustang or muscle car, there’s a certain case for keeping it looking as period correct as possible. But given the advances in technology, it’s often a great idea to add a dash of modern reliability. Peter Klutt, who owns and operates noted muscle and classic car specialist Legendary Motorcar Company, was faced with a bit of a problem around a decade ago. “A lot of the cars that we service and restore are concours-type vehicles, where factory-correct appearance is paramount, but we began to see that more and more owners actually wanted to drive their cars. One of the biggest issues was the battery. While original flooded cell batteries looked great, they were none too reliable and costly to replace. One day, out of frustration, I decided to cut the top off an old flooded-cell battery and examine the top. We then came up with the idea of making a traditional style lid that fits over the casing of a modern VRLA battery. We got a patent and started making them, primarily for muscle cars and classics. Currently we offer them for Chrysler, Ford and GM muscle cars and other collectible automobiles from the 1950s to the early ’70s. These come with the correct style maintenance caps, tags and finish on the top of the battery, plus in some cases, extenders for the terminals, which is perfect for those enthusiasts who want a period correct look under the hood. So far we’ve seen quite a steady demand for them.”

Editor’s Note: Special thanks to Daryl Brockman and Becky Pias at Johnson Controls as well as Peter Klutt at Legendary Motorcar Company and Adrian Chadwick at Westward Wind Productions.

Optima Batteries Inc.
(888) 867-8462

Legendary Motorcar Company Ltd.
(905) 875-4700

Exide Technologies
(678) 566-9000


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