Forget gasoline or ethanol.

Your car doesn’t run on petrochemicals; it runs on electricity. And for the most part, the power source in that car is a battery (or two). Over the years, battery technology has advanced rapidly. Because of this, we figured the time was ripe to take a closer look at the world of high performance batteries.

What type of battery does your car require?

Batteries are rated by capacity. This is the amount of electrical current or amps a battery can supply for a specific length of time.

Older battery ratings revolved around “Ampere Hour” ratings, but the newest rating system is the “CCA” (Cold Cranking Amps) or “CA” (Cranking Amps) system. Amp Hour (AH) is easy to figure out, but the others are not. XS Power Batteries offers some insight:

“People often wonder what the term ‘Amp Hours’ means when referring to batteries. Many people assume that AH is a standardized rating for a battery’s ability to discharge current — a true statement. The actual method for determining the AH rating is more often not fully understood by the automotive enthusiast.”

Measured in hours, AH is most commonly used to rate deep-cycle batteries or any type of battery used for relatively low discharge rates for extended periods. Most batteries, including XS Power batteries, are tested in a 20-hour cycle. AH tests can be performed for 10-hour cycles at a higher amp load, but results are not as useful for determining long-term capacity.

Cranking Amps determines the battery’s capability of delivering current (amps) at 32-degrees F. This rating will generally range from 250 to 800 amps or higher, but keep in mind that some CA ratings can prove optimistic.

Compare RC Ratings to Make a Good Choice

To combat any confusion surrounding battery ratings, compare the “RC” or Reserve Capacity ratings of the batteries in question. This rating determines how long the ignition and other electrical components can be operated by the battery alone.

The RC rating is defined as the number of minutes a new, fully charged battery at 80 degrees F can be discharged at 25 amps and maintain a voltage equal to or higher than 1.75 volts-per-cell. This works out to 10.5 volts for a 12-volt battery.

For example, we have an Energizer Group 75 battery in one of our vehicles. It has an RC of 100 minutes. We also have a big Delco Group 24 battery we keep charged as a booster. It has an RC of 130 minutes. At the top of the heap is the XS Power AGM battery shown in the photos. It has an RC of 135 minutes.

High-powered ignition systems create added loads on the battery along with the charging system. When you increase the demand on the battery, it should be able to handle the load. Amp Hour ratings are important here. The big XS Power S3400 battery we’re using has an AH rating of 65.

How does a battery’s AH rating work with ignition components and other electrical “draws” in racecars?

According to MSD Ignition, operating time decreases as engine rpm increases. The smallest dedicated battery for use on a MSD 6 or 7 series ignition system is a 12-AH package. As an outer limit example, if you use the monster MSD 8 series ignition box in a racecar and you use it at full bark (12,000 rpm), there’s a current draw of 36 amps!

(story continues below slideshow)
three automotive car batteries in a row
a collection of automotive batteries
close up of warning label and specs of an xs power battery for a car
car battery next to tape measure for width
a car battery on a scale to measure weight
car battery with terminal removed
adjustable automotive battery terminal hardware
a close up of an automotive battery terminal
allen wrench used on an automotive battery terminal
vintage automotive battery charger
moroso battery charger

There are all sorts of batteries out there – some good, some not so good. In this bunch, we have a Group 75 battery that barely starts a stock 1986 305-powered Monte Carlo; a more potent Group 24 battery we use as a booster battery and a honking S3400 AGM battery from XS Power.

The labels affixed to batteries are important. Typically, they’ll include CCA (Cold Cranking Amps) or CA (Cranking Amps) and in most cases, they’ll include RC (Reserve Capacity). Today, battery manufacturers seldom list the more important (to us) Ah (Ampere Hour) rating. More about this in the text.

XS Power’s big S3400 has a maximum amp rating of 3300. The Cranking Amp rating is 1000 Amps (!) while the Reserve Capacity is 135 minutes.

This is a big brute of a battery (perfect for starting a big stroker motor on the street). It measures 10.28-inches in length, 7.24-inches in height and 6.75-inches in width. Note however the base of the battery is slightly smaller, which allows it to fit into more common battery trays.

This is no small battery. It tips the scales at 47-pounds. In comparison, however the Group 24 Delco battery we mentioned elsewhere weighs 39 pounds on our bathroom scale.

Upstairs, the battery posts bolt on. They come with a top post adapter (shown in the second photo). There are a number of optional bolt-on terminal packages available from Summit Racing, including side-terminal kits and kits for trunk mount battery applications (shown in the last photo).

Here’s the top post kit installed on the battery. It’s held in place with a 6-mm Allen-head cap screw. XS Batteries recommends 8-foot pounds maximum torque when installing the terminals.

You cannot use any old-fashioned charger on an AGM style battery. These battery chargers were designed solely for flooded cell batteries, and they will damage an AGM battery.

XS Power recommends the charger produce no more than 2.45 Volts per cell. The Moroso # 74016 Charger shown here has a voltage limit of 2.42 volts per cell (on the regular setting). If your battery charger does not meet the required maximums (set out in the text), you’ll need to upgrade. Summit Racing offers all sorts of options, including dedicated XS Power chargers.

There are additional considerations as well, such as other electrical components in your car. Today’s car are highly sophisticated. Large-capacity electric fuel pumps, electric water pumps, electric fans, electric (or solenoid) shifters, throttle stops, and even small things like shift lights, gauge lamps, and other hardware deplete power and AH from the battery.

Because of this, you must first determine how many amps (AH) each of the electrical “accessory” components draws continuously from the battery. For example, you might be “shocked” to find that a large billet electric fuel pumps can draw 8 AH or more.

Once you’ve determined each component’s AH draw, add up the total AH figures. Using the following chart from MSD, you can then determine the total AH draw of a typical high-powered ignition system at a specific engine rpm.

Ignition Amp Use

             RPM (V8 Engine)                                           MSD 6 & 7 Series


3,000                                                                         3

4,000                                                                         4

5,000                                                                         5

6,000                                                                         6

7,000                                                                         7

8,000                                                                         8

9,000                                                                         9

10,000                                                                       10

11,000                                                                        11

12,000                                                                       12


The following is a sample AH draw. In the example, pretend the engine sees a maximum rpm ceiling of 8,000. The math is easy.

Electric fuel pump:                          8 amps

Electric water pump drive:            5 amps

Other accessories:                           12 amps

Ignition requirements:                   8 amps


Total:                                               33 amps


Next, multiply the total electrical requirements by the duration of time it must operate without a battery recharge. This is particularly important for racecars without charging systems.

Keep in mind we’re not talking about just seven- to 10-second quarter-mile runs. Consider the time spent in the staging lanes, doing a burnout, staging time, driving down the return road, etc. In this case, a safe figure might be 1/2 hour. Multiply the amp requirement by the time.

33 amps X 1/2 hour = 16.5 AH

Now, the final step in the equation: starting the car. To determine just how many amps it requires to start the car, multiply the final amp requirement figure by a factor of at least three:

16.5 AH X 3 = 49.5 AH

The final 49.5 AH number is the absolute minimum size of battery required for our hypothetical electrical load example. Essentially, it’s what you need to start your car. And if you have a street/strip car with a lot of power under the hood and plenty of on-board electrical equipment, you might need a bit more.

Comparing Lithium Batteries and Absorbent Glass Mat (AGM) Batteries for High Performance Applications

For high performance applications, the best bets are AGM (Absorbent Glass Mat) batteries or Lithium batteries.

Lithium batteries are powerful and can offer tremendous power storage capability. Certain examples can also be considerably lighter than their lead-acid based battery cousins. But they have a couple of downsides as well.

Lithium batteries can be dangerous if not monitored properly, and they tend to be expensive. That puts them out of reach for most of us.

Which leaves us with AGM batteries. XS Power Batteries says:

“The XS Power 12-volt performance battery is a six-cell, sealed-valve regulated, lead-acid battery. Sealed-valve regulated lead-acid batteries are manufactured in two types — gel-cell and AGM (Absorbent Glass Mat). The key difference is how the electrolyte is suspended between the lead plates. AGM batteries, such as the XS Power 12-volt performance batteries, use a fibrous material to suspend all liquid electrolyte against the plates. Even if the case were ruptured, no acid would leak. In contrast, gel-cell batteries suspend the electrolyte in gel form and are not necessarily leak-proof.”

According to XS Power, AGM batteries are similar in chemical function to flooded and maintenance-free batteries in that they convert electrical energy into chemical reactions on the lead plates. However, AGM batteries have substantially less electrolyte (a mix of sulphuric acid and water) than a typical flooded or maintenance-free battery.

AGM batteries can operate with less acid because each battery cell operates on positive-charged air pressure, which allows for the water produced during discharge to condensate and recycle inside the battery. As a result, almost no gasses escape the battery under proper charging conditions. And if the battery were to be overcharged (the main cause of AGM failure), the small amount of electrolytes could be “gassed” and vented by the battery’s safety valves. (Editor’s Note: See the section on charging below).

The cells inside are compressed before insertion into the AGM battery case, which increases performance and makes the battery extremely vibration resistant. The reduced acid content of the battery allows for additional plates and therefore additional performance in the 12-volt configuration.

So why do high-quality AGM batteries cost so much more than a standard flooded battery? According to XS Power:

“XS Power batteries are manufactured using only virgin lead, 99.99 percent pure compared to most batteries that use recycled lead. The pure-lead design means better performance. Grids are thinner. This allows for more grids, which means more surface area in a smaller package. More surface area means more power. Absorbed Glass Mat design means longer life, vibration resistance, and they can be mounted in any position except upside down.”

What about “deep cycle” batteries?

While race cars equipped with high-output ignition systems work well with deep-cycle batteries, this isn’t the case for cars fitted with a charging system. Deep-cycle batteries are designed to withstand repeated discharge and recharge cycles.

Although a deep-cycle test is perhaps the toughest of any when discussing batteries, the specific use of these types of batteries actually precludes them from use with a charging system. Deep-cycle batteries aren’t well-suited for day-to-day activities like cold-weather startups.

Deep-cycle batteries are the best choice for a drag car, though, because you’re constantly depleting and replenishing the batteries. This regular discharge-charge cycle can wreak havoc on standard batteries.

Today’s ignition systems require at least 12 volts to produce an optimum spark; however, in some drag-race applications, it might be a good idea to switch over to a 14- or 16-volt system. That’s because a high performance battery cell produces a maximum of approximately 2.15 volts-per-cell open circuit, or 12.9 volts total. As soon as a load is placed on a 12-volt battery, the voltage per cell will drop rapidly to two volts per cell or 12 volts total. Operating below this voltage level often results in ignition problems such as a high-speed miss. Add in that reduced voltage will also negatively affect the starter and it’s ability to spin the motor, and it’s easy to see why many race cars need additional voltage over a conventional 12-volt system.

We must also account for the increased amount of electronics on race vehicles these days. As things like on-board computers and delay boxes become more prevalent, the amp-draw loads continue to increase. This only helps to shorten the amount of time it takes for a 12-volt battery to drop to marginal voltage levels. Fourteen- and 16-volt batteries provide a two- to four-volt cushion to the electrical system over a 12-volt system. Even when totally discharged, a 16-volt battery can produce 14 volts as opposed to a 12-volt discharged battery producing only 10.5 volts. This easily exceeds the minimum recommended voltages of a racing ignition even when totally discharged.

Fourteen- and 16-volt batteries can also deliver improvements in performance. Higher voltage batteries allow the starter motor to spin faster and increase the performance of electric fans and pumps. In addition, a 16-volt battery can help to fire massive plug gaps and pave the way for increased jet sizes over a 12-volt baseline. Some racers even report that due to the hotter spark, engines running 14- or 16-volt systems don’t seem to fall off as much in “bad air” as when using 12 volts.

Which components can you use with a 16-volt system?

  • Ignition: Most racing ignitions on the market need at least 12 volts for proper operation and will benefit from an increase in battery voltage. The more input voltage to the ignition, the greater the output. The hotter spark from a 14- or 16-volt battery running through a high-powered ignition system allows racers to use increased plug gap, which can allow for increased jet sizes.
  • Starter: 14 or 16 volts will spin the starter as much as 30 percent faster than 12 volts.
  • Electric Fans: The electric fans will also spin 10 to 15 percent faster with no damage to the fan.
  • Electric Water Pumps: The water pumps will also spin 10 to 15 percent faster resulting in quicker cooling.
  • Electric Fuel Pumps: Adding voltage will build more pressure at the pump. Although additional pressure isn’t required, the extra pressure can be backed down at the regulator if desired.

Some racing components aren’t compatible with increased voltage; however, many 12-volt components will operate just fine on 16 volts. That’s because a 12-volt component is actually designed to be subjected to as much as 15 volts when used with a 12-volt alternator. Over the years, many racers have run 14- or 16- volt systems and few found it necessary to use a resistor on any components.

The following items have been successfully run on 16 volts, but a resistor may be required to step down the voltage in some cases:

  • Transmission Brake
  • Delay Box
  • Timers
  • Throttle Stop

Some alternators are engineered to work with 14- or 16-volt batteries. There are also battery chargers that will charge an AGM battery properly.

XS Power says this about charging its 12-volt AGM batteries:

  • Charge voltage is not to exceed 14.4V total for extended periods of time (5 minutes max).
  • The charger used must have an automatic shut-off. Some AGM chargers may climb to a maximum voltage of 15.5VDC for a short period of time (usually less than 5 minutes) but will resume charging at or near 14.4VDC ± .3VDC for the duration of the charge cycle. If you are unsure of your charger’s capabilities, contact the manufacturer.
  • Exceeding 14.4VDC ± .3VDC will cause the battery to “gas,” and once the oxygen is released from the battery, there is no way to restore it. The permenant results will be reduced capacity and battery life. This type of damage will cause the battery to show a proper open circuit voltage yet won’t accept a charge. It will become excessively hot during charging. This kind of damage will void the warranty. Therefore, ensure that your battery charger won’t exceed 14.4VDC ± .3VDC at any time during the charging cycle. For ease of use, we recommend recharging the battery with an XS Power Intellicharger p/n 1005, as it is a totally automatic three-stage microprocessor-controlled battery charger with float charging capability. This battery charger prevents overcharging, maintains proper performance and can be left on the battery indefinitely during non-use periods.
  • It is very important to never use a charger designed for flooded 12-volt batteries, not even once with a XS Power 12-volt AGM battery. Furthermore, we recommend disconnecting the battery from the rest of the vehicle’s electrical system during charging.
  • All lead-acid batteries, both flooded and AGM designs, are subject to self-discharging, and this self-discharge rate is affected greatly by ambient temperature in which the batteries are stored. Higher ambient temperatures will discharge the battery faster. Cool storage for batteries is the best. When voltage is lower than 12.6-volt or storing time is longer than six months, the battery must be recharged.

For 14-volt or 16-volt batteries, XS Power notes the charge voltage should not exceed 2.45 volts per cell ± .05V for extended periods of time. Some AGM chargers may climb to a maximum voltage of 21 volts for a short period of time, and then they will drop down to the 2.45 volts-per-cell figure. The balance of the above instructions for a 12-volt battery apply, but you must take into consideration the extra number of cells in a 14- or 16-volt battery.

In the end, it’s easy to see there is much more to high performance batteries than meets the eye. In a future post, we’ll take a detailed look at mounting, cables and other accessories to maximize battery performance.

Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.