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.