process may be repeated. Some vehicles use other starter batteries. For weight savings, the 2010 Porsche 911 GT3 RS has a lithium-ion battery as an option; from 2018 onward, all Kia Niro conventional hybrids feature one as well. Heavy vehicles may have two batteries in series for a 24V system or may have series-parallel groups of batteries supplying 24V. Specifications Physical format Batteries are grouped by physical size, type and placement of the terminals, and mounting style. Amp hours (Ah) Ampere hours (Ah or A·h) is a unit related to the energy storage capacity of the battery. This rating is required by law in Europe. The ampere hour rating is generally defined as the product of (the current a battery can provide for 20 hours at a constant rate, at 80 degrees F (26.6 °C), while the voltage drops to a cut-off of 10.5 volts) times 20 hours. In theory, at 80 degrees F, a 100 Ah battery should be able to continuously provide 5 amps for 20 hours while maintaining a voltage of at least 10.5 volts. It is important to realize that the relationship between the Ah capacity and the discharge rate is not linear; as the discharge rate is increased, the capacity decreases. A battery with a 100Ah rating generally will not be able to maintain a voltage above 10.5 volts for 10 hours while being discharged at constant rate of 10 amps. Capacity also decreases with temperature. Cranking amperages (CCA, CA, MCA, HCA) Cold cranking amperes (CCA): the amount of current a battery can provide at for 30 seconds while maintaining a voltage of at least 7.2 volts. Modern cars with computer controlled fuel-injected engines take no more than a few seconds to start and CCA figures are less important than they used to be. It is important not to confuse CCA with CA/MCA or HCA numbers as the latter will always be higher due to warmer temperatures. For example, a 250 CCA battery will have more starting power than a 250 CA (or MCA) one, and likewise a 250 CA will have more than a 250 HCA one. Cranking amperes (CA): the amount of current a battery can provide at , again for 30 seconds at a voltage equal to, or greater than, 7.2 volts. Marine cranking amperes (MCA): like CA, the amount of current a battery can provide at , and often found on