What Is Battery Reserve Capacity?
Commonly referred to as RC, reserve capacity is the amount of time, in minutes, that a 12V battery can run before dropping to 10.5V. It is measured in reserve minutes. For example, if a battery has a reserve capacity of 150, that means it can supply 25 amps for 150 minutes before the voltage drops to 10.5V.
Reserve capacity differs from amp-hours (Ah) in that reserve capacity is simply a measure of time, whereas amp-hours measure the number of amps, or current, that can be produced in one hour. You can calculate reserve capacity from amp-hours, and vice versa, as they are related, but they are not the same thing. When comparing the two, RC capacity is a much more accurate measurement of how long a battery will last under sustained loads as opposed to amp-hours.
Why is battery reserve capacity important?
Reserve capacity is used to understand how long you can run your batteries with consistent loads. It becomes very important to understand if you intend to discharge your batteries for a longer period of time and it is a great indicator of battery performance. If you know your reserve capacity, you will have a better understanding of how long you can use your batteries, and how much power you will be able to leverage. Whether you have a reserve capacity of 150 minutes or 240 minutes is a big difference and can drastically change how you use your batteries as well as how many you may need. If you’re spending a full day on the water fishing, for example, you should know how much power and time you’ll have with your battery so that you can time your travel effectively and get home without running out of juice.
Reserve capacity directly impacts the power you are able to generate with your battery. Since power is equivalent to amps multiplied by volts if your battery voltage drops from 12V to 10.5V, the power drops. Also, since energy is equivalent to power times the length of time used, if the power drops, so does the energy produced. Depending on how you intend to use your battery - such as for days-long RV trips, or for an occasionally used golf cart, you will have different reserve capacity needs.
Learn more about how reserve capacity differs between lithium and lead-acid batteries.