All current consumer automotive systems depend on a battery to run. There are several types on the market for different applications, each vying to be the ultimate solution for what appears to be the future: electric vehicles. Electric car batteries may on the surface appear to be similar to the 12V lead-acid battery of yore, but there is more than meets the eye.
Leading the Charge
In a conventional gasoline engine, the battery provides the initial energy required to turn the starter, which in turn starts the engine’s internal combustion system. These lead-acid batteries are rated by Cold Cranking Amps (CCAs — the amount of current a battery can provide at 0°F for 30 seconds) and Reserve Capacity (RC—amount of time a battery can provide 25 amps while keeping voltage above 10.5V). Together, these ratings provide information on how much power is available and for how long. Gas engines require a lot of energy at start-up, but after that, the battery is recharged and maintained by the alternator, so it can “relax” a little without sustained effort or becoming too drained. Therefore, the higher the CCA, the better.
Batteries for electric vehicles (EV) however, need less energy at start-up and more during operation. They must provide power over a sustained period of time, have the ability to discharge to very low levels between chargings and be able to handle recharges on a regular basis without wrecking the battery internally. Therefore, it’s important for electric car batteries to have a higher RC rating.
The typical 12V lead-acid battery is composed of 6 cells, each providing 2.1 volts through a chemical reaction between a submerged lead plate and the surrounding acidic environment. Lead-acid batteries powering gasoline engines have thinner plates, which allow for faster movement of more electrons (more energy) during start-up, but this design will fail quickly under repeated heavy discharge. The lead-acid batteries in electric cars have thicker plates, which don’t give the same oomph in the beginning, but allow them to discharge more slowly and deeply, with the ability to recharge many times without killing the battery. For this reason, they are called “deep cycle batteries.” In addition to a slightly different internal makeup, electric car batteries require more cells, or what ends up looking like one giant battery.
The battery is key in the race to design the perfect electric vehicle. Because of their size and density, they make up the majority of the vehicle’s weight and cost. Manufacturers keen to market their vehicles to the general public are exploring different technologies to be lighter, more efficient and cheaper. Several have adopted lithium-ion batteries like those found in laptops and cell phones. These produce more energy, have a slower self-discharge and perform better under high temperatures. However they are more dangerous if damaged, still leave something to be desired in terms of overall life cycle and are more expensive. A few companies are developing lithium-based hybrids to mitigate these problems. Hybrid vehicles use a combination of traditional automotive batteries and newer technologies to try and provide the best of both worlds.
One last word of caution: lead-acid batteries designed for gas engines should not be used in electric vehicles, even in series. They may on the surface appear to be the same, but their internal structure simply cannot stand the heat and power requirements of an electric vehicle.
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Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.