The battery of a race car is mostly out of sight and out of mind, until it doesn't work. To learn more about something so common as a battery, and which ones may be best for race cars, Stock Car Racing recently spoke with Gale Kimbrough, technical services manager for Interstate Batteries.

SCR: How does a battery work?
Kimbrough: A battery stores electrical energy. It contains chemicals capable of producing electricity on demand. In our case, that means a lead object submerged in an acid. The lead is shaped to form a negative and a positive grid. These grids are pasted with a chemical after which they become plates. The negative plate is placed in a porous polyethylene sleeve called an envelope separator. These sleeves separate the lead grids from each other. This is necessary to keep the plates from touching each other. Were they to do so, it would cause a short, reducing the battery's capacity. The use of these sleeves has been a great improvement in vibration and impact resistance. In the end, all the plates are connected by lead straps to the terminals outside the battery.

SCR: Which battery do we need in a race car, since it will see some rather rough use, including vibration and impacts?
Kimbrough: First, there are two circumstances. One or the other is found in most stock cars. There are those with a charging system, such as an alternator, and those without. We consider a battery to be fully charged at a level of 12.66 to 12.75 volts and to be discharged at 11.90 volts. This is known as the battery's "state of charge" as checked with no load by an accurate voltmeter.

These numbers will change drastically when the battery is put under a load, such as starting a high-compression engine. Batteries are rated by cold cranking amps (CCA) and cranking amps (CA). CCA is a truer indicator of battery capacity as it rates battery strength at zero degrees Fahrenheit. The battery with a higher CCA rating will be heavier than one with a lower rating. In many stock cars, this weight can be a factor. Yet, don't be too quick to choose a small battery. Placing a battery for the best weight distribution can make up for some extra weight.

This is a bad scene. An emergency clamp is used on one post, and it appears to have been there long enough to generate corrosion. One cable end is sufficiently corroded to cause cranking problems. In addition, the charging system seems to be malfunctioning. The black, boil over crud on top of the battery indicates an overcharging condition.

This is an emergency clamp. It should be used for only a short period of time and then replaced with a crimped-end connector on a new cable. The emergency clamp does not have the current carrying capacity or the corrosion resistance of the crimped-end/soldered connection.

Generally speaking, a battery of 525 CCA will probably start and run a Street Stock-type of car for the night without an alternator. This is with the understanding your engine starts easily. This won't necessarily be true in other classes with high compression engines. Check a battery in a car similar to yours at the end of a night's worth of racing. Use a good voltmeter. It should be at least 12.00 volts. If so, then this is an adequate size battery for your use. If you use an alternator, a slightly smaller battery may be used. Here you will be using up more "Reserve Capacity" (RC) to start the engine, but the alternator will soon be recharging the battery to a point of maintaining proper voltage for the ignition.

SCR: What if you're not using a charging system?
Kimbrough: The RC of a battery becomes important. Most electronic ignitions need more than 10.5 volts to operate properly. Most batteries don't have the RC on the label. However, if you look in the dealer's book, the RC is listed for all batteries. Remember, the drain of the starter will use up some of this RC each time the engine is started. A 200-amp load imposed by the starter is not uncommon. If the engine starts in 3 seconds, good. If it sometimes takes 30 seconds of winding the starter and heating the cables to get your engine going, this is a sign you may need the insurance of a greater capacity battery.

It is very important for the starter to have adequate power going to it during the starting process. At the instant of electrical contact between the battery and the starter, the battery voltage drops drastically for about 11/43 of a second or so, then it rebounds. When battery voltage is in a low state of charge, or the battery is too small for the job, it does not rebound as it should. Thus, low voltage overheats the starter and the engine turns slowly. Three things can happen here. First, the engine won't start. Second, another larger battery may be needed. Third, the starter itself may be damaged by low voltage and heat. So the battery needed in your race car must have the CCA capacity to start your engine and the RC to maintain ignition voltage. We have made great advances in vibration/impact resistance over the years. The polyethylene sleeve, among other technical advances, has helped automotive batteries to live well in racing applications.

SCR: What about batteries that appear to have dry cells, the ones that look like a battery pack?
Kimbrough: These are especially good when extreme vibration and impact resistance are a prime consideration. They are referred to as Optima AGM batteries. AGM stands for absorbed glass mat. In these batteries each cell (6 in a 12v. battery) is spiral wound with layers of glass mat and lead grid. The acid is absorbed by the glass mat. When tightly wound, there is virtually no internal place in the battery where movement can occur. As such, this type of battery can resist more impact than a conventional battery and still keep functioning. Another factor for race car use is that the AGM can be mounted in any position. While it is lighter, it is also priced somewhat higher than a conventional battery.

SCR: Let's talk about connections and corrosion. This seems to be a never ending problem. What is your advice?
Kimbrough: We need to start by getting all the battery connections clean. This can be done several ways. There are mechanical cleaners that scrape or wire brush the inside and outside of the terminals. A pocketknife should not be used for this purpose. The mechanical cleaners leave a surface in the same shape, round and tapered, as originally made. A soda wash with a small brush can be used to remove all the corrosion. Common baking soda, mixed 50/50 with water, will do. Although it may seem to do so, your favorite cola doesn't really do that good a job. The key with any terminal connection is to get it completely clean.

The original shape must be maintained to achieve full contact between the post and clamp. Any time a battery is replaced, the clamps on the cable connections should be cleaned properly. Many a "battery" problem turns out to be a connection problem. The best way to prevent corrosion on a battery is to seal the connections. A good connection can be sealed with a spray protectorant or with a high-temperature electrical grease. With the spray it might be difficult to coat the underside of the connection. In this case use a small brush to complete the job. If grease is used as a sealer, it should be a type made for electrical connections. During the life of a battery, the connections often get hot. Ordinary grease can liquefy under these conditions. It can then run down inside the connection and insulate the post from the clamp. Again, this is not a visible problem.

SCR: We've seen people who often are using the emergency connector. Any problems with that?
Kimbrough: These are the connectors with a bolt-down clamp for the wire. When a corroded terminal fails, use one of these to get home. The biggest problem here is the lack of contact in the connection. The strap is steel and not as conductive as the all-lead connection. Also these connectors are more prone to corrosion. Far too much of the cable, which is copper, is exposed to the air. Moisture in the air, especially salty air, causes corrosion to form. Corrosion can even extend up inside the cable insulation and cause a hidden problem.

SCR: How bad is it for battery life to let the battery stand in an uncharged or dead state?
Kimbrough: All batteries self discharge. A battery will lose 3 to 5 percent of its charge per month just sitting on the shelf. If it sits too long, the battery life expectancy is reduced. When purchasing a battery, do so from a company which insures its batteries are fresh. One easy way to damage a battery is to discharge it and then to store it without it being recharged.

Interstate Batteries
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