Deep cycle batteries are primarily rated by their Amp-hour (Ah) capacity, indicating how much current they can deliver over a specific period, typically 20 hours.
Here's a breakdown of how deep cycle batteries are rated:
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Amp-Hour (Ah) Rating: This is the most important rating for deep cycle batteries. It represents the amount of current the battery can deliver continuously for a specified number of hours, usually 20 hours, until it is considered fully discharged. For example, a 200Ah deep cycle battery should be able to deliver 10 amps continuously for 20 hours (200Ah / 20 hours = 10 amps).
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Reserve Capacity (RC) Rating: This rating indicates how long a fully charged battery can deliver 25 amps continuously at 80°F until the battery voltage drops to 10.5 volts. It's expressed in minutes. A higher RC rating suggests the battery can power essential accessories for a longer duration if the charging system fails.
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Voltage: Deep cycle batteries typically come in 6V, 8V, or 12V configurations. The voltage must match the requirements of the application.
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Cycle Life: Deep cycle batteries are designed to be repeatedly discharged and recharged. The cycle life rating indicates the approximate number of discharge/recharge cycles the battery can withstand before its performance significantly degrades. This is often presented as a graph showing depth of discharge (DOD) vs. cycle life. A shallower depth of discharge (e.g., only discharging the battery to 50% of its capacity) will typically result in a much longer cycle life than repeatedly discharging the battery to 80% or more.
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Depth of Discharge (DOD): This refers to the percentage of the battery's capacity that has been discharged. Deep cycle batteries are designed to tolerate deep discharges, unlike car batteries, but even with deep cycle batteries, regularly fully discharging them will shorten their lifespan.
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Cold Cranking Amps (CCA): While more relevant for starting batteries, CCA is sometimes listed. It refers to the number of amps a battery can deliver for 30 seconds at 0°F while maintaining a voltage of at least 7.2 volts. Though deep cycle batteries aren't primarily designed for starting applications, a higher CCA rating can be beneficial in cold climates.
Key Differences from Car Batteries:
Unlike car batteries, which are designed to provide a short burst of high current to start an engine, deep cycle batteries are designed to deliver a sustained current over a longer period. Car batteries have a relatively low Ah rating compared to deep cycle batteries. This is why using a car battery in an application requiring deep cycling will quickly damage it.
In summary, deep cycle batteries are primarily rated by their Ah capacity, reflecting their ability to provide sustained power for extended periods. Other ratings, such as reserve capacity and cycle life, provide additional information about their performance and durability.
