Automotive lead-acid batteries have certain ratings that the manufacturer usually prints on the label. These ratings specify how much power the battery can deliver under specified conditions, which of course affects the battery price.
The three most common ratings of interest are
- CCA – Cold Cranking Amps
- RC – Reserve Capacity
- Ah – Ampere hours or amp-hours.
These ratings have been defined by the Battery Council International (BCI) to provide uniform standards.
CCA – Cold Cranking Amps
According to Interstate Battery System International (Marine/RV Battery Maintenance, Publication 200004-CS, May 2009), CCA is defined as the amount of current in amperes that a battery at 0° F (-18° C) can deliver for 30 seconds while maintaining at least 1.2V per cell (that's 7.2 V for a 12V battery).
This rating applies mostly to starting/lighting/ignition (SLI) batteries as it is a rating of how well the battery will turn over an engine under moderately cold conditions. As the temperature drops, the cranking capacity of the battery is reduced, so the higher the CCA number, the better the battery can be expected to perform in extreme cold.
Similar Ratings: MCA ( Marine Cranking Amps) and HCA (Hot Cranking Amps)
Similarly, there are other cranking ratings that differ only in the temperature specification. In all cases, it is the current delivered for 30 seconds.
Marine Cranking Amps (MCA)
MCA is the amount of discharge current a battery can deliver at 32° F (0° C) under the same criteria as the CCA. The MCA rating may be found on deep-cycle RV/Marine batteries. Again, the higher the number, the more power the battery can deliver under the specified conditions.
However, because a battery is more efficient at the warmer temperature, the MCA will be higher than the CCA – the Interstate Battery Terms Glossary calls it an "artificially high rating" – and it is important not to confuse the two.
Hot Cranking Amps (HCA)
On the same topic, some batteries may list a HCA (Hot Cranking Amps, sometimes called just Cranking Amps or CA) rating similar to CCA that defines the current output at 80°F (27°C). Again, this rating will be higher than the CCA and the two ratings must not be confused.
According to Interstate, temperatures above 90°F (35°C) will adversely affect battery life and performance.
RC – Reserve Capacity
Of importance to RV owners when considering coach batteries, this rating is the number of hours over which the battery can deliver 25 Amps of current (at 80°F / 27°C) without falling below 1.75 Volts per cell. That's about 88% of its capacity, or 10.5V on a 12V battery.
Reserve Capacities will vary widely, depending on many factors a general purpose battery may last for only an hour or two at that rate of discharge, while an expensive deep-cycle battery for solar or industrial use may last six or seven hours. The larger the number, the greater the storage capacity of the battery.
Some manufacturers may use a lower discharge rate than 25A. At lower discharge rates, the battery will of course last longer. At 5A of current drain, for example, the batteries cited above may last up to 12 hours and 45 hours, respectively. When evaluating a battery, check to see what discharge rate is used in calculating the RC. This information may not be on the battery label but may be available from the dealer or from the manufacturer's web site.
A deep cycle battery is allowed to cycle to about 50% of its capacity (any more will reduce battery life), giving it a greater reserve capacity in reality if not in rating.
Ah – Ampere hours or amp-hours
This is another measure of the storage capacity of a battery. It is the inverse of RC, being instead the amount of current that a battery can deliver for a specified number of hours without dropping below 1.75V/cell. The BCI standard is for a 20 hour discharge at at 80°F / 27°C.
A battery that can deliver 5A of current for 20 hours has a 100Ah (5A x 20 hours = 5Ah) rating, while one that can deliver 10A of current has an Amp-hour rating of 200Ah. Again, the higher the number, the better the storage capacity of the battery.
The specifications commonly used for a lead-acid automotive battery – CCA, MCA, RC, and Ah – are important and useful information for selecting a battery. While most owners will trust that battery department to select and install the proper product, a little background knowledge is always useful.
More on Deep Cycle RV Batteries
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Thomas Alan Gray - Tom has been writing for over 30 years; curiosity leads him to dig into a wide variety of topics.
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