What is Reserve Capacity on a Battery? Understanding Reserve Capacity vs Amp Hours

If you’ve been battery shopping lately you know that some batteries seemed to be measured by Reserve Capacity and others in Amp Hours. We’ll break down the difference so you can shop with confidence!

Did you know that understanding the reserve capacity (RC) and amp hours of a battery can help you make informed decisions about selecting the right battery for your vehicle, RV, or boat? In fact, knowing these metrics can even save you from unexpected battery failures in critical situations. 

In this post, we will explore the concepts of battery reserve capacity vs amp hours, their differences, and their importance in various applications - including answering the question: what is reserve capacity on a battery? 

By the end of this post, you will have a deeper understanding of reserve capacity and amp hours, as well as how to measure, determine and choose the right battery for your needs. Let's get started!

KEY TAKEAWAYS

• Reserve capacity (or RC rating) is most commonly found on lead-acid batteries and not lithium or AGM batteries. 
• Reserve capacity is a measure of the time, in minutes, that a 12V battery can run before needing to be recharged or replaced.
• Battery reserve capacity rating and amp hours are important metrics for assessing a battery's stored energy, particularly in fishing, marine and RV applications.
• Cold Cranking Amps (CCA) and RC rating should both be considered when selecting the right starter battery type for your vehicle.

What Is Reserve Capacity

A battery reserve capacity, or reserve capacity rating, is a measure of the time, in minutes, that a 12V battery can run at 25 amps before its voltage drops to 10.5V. 

It is a crucial metric that helps you understand a battery's ability to deliver energy over time without relying on the vehicle's charging system and gives an apples-to-apples comparison among many traditional lead-acid batteries for how much power each battery has. 

In other words, the battery capacity rating tells us how long a fully charged battery can provide power before needing to be recharged or replaced.

To calculate the reserve capacity of a battery, it must first be fully charged. Manufacturers draw 25 amps of power from the battery at 80°F. When the voltage drops below 10.5 volts, they stop drawing power. The duration of time this process takes is the battery's reserve capacity, which is measured in minutes.

Reserve capacity is particularly important for lead-acid batteries, which are commonly used in vehicle applications. At 10.5 volts, a lead acid battery is considered “dead,” which makes this a crucial metric when choosing the proper battery.

Thus you should consider the RC rating in a lead acid battery to be the maximum amount of energy available rather than a standard. 

But battery reserve capacity also applies to lithium batteries, which will provide enough power to go beyond that of traditional lead acid batteries. This is because lithium batteries, such as each of our products, have superior technology and design that allows them to reach the deeper depth of discharge without causing significant harm to the battery. 

However, most lithium batteries, including all of those in our ProConnect Series and Baja Series, do not publish the battery RV rating, but rather the amp hour measurement is used to describe battery capacity. 

Read Next: Understand why you should consider switching to lithium batteries. 

Battery Reserve Capacity vs Amp Hours

While reserve capacity is an essential aspect of knowing how much battery power a particular battery has, it is not the only metric to consider. It is important to understand both reserve capacity and amp hour rating, as they provide different perspectives on a battery's performance and power delivery.

The amp hour rating is a critical measure that plays an important role, and is often more common than the RC rating. While RC rating is a measurement of time, an amp hour rating is the measurement of how many amps the battery can provide in one hour. 

Reserve capacity is measured in minutes, whereas amp hours are measured in amps per hour. 

To convert reserve capacity to amp hours (AH), one must divide the reserve capacity by 60 and multiply the result by 25.  

Ah = (RC / 60) x 25

Conversely, to convert amp hours to reserve capacity, one must divide the amp hours (AH) by 25 and multiply the result by 60.

RC = (Ah / 25) x 60

Understanding the relationship between these two measurements is crucial for accurately assessing a battery's capacity and performance in various applications and making comparisons between two vehicle batteries.

Read Next: Refresh yourself on what are amps. 

Why is Battery Reserve Capacity Important

Knowing the reserve capacity of a battery is vital because it indicates how long a fully charged battery can provide power without relying on having the vehicle running. This information is especially useful in applications such as fishing and marine, where consistent energy is required, and RVs, where long-term power is essential. 

By understanding both reserve capacity and amp hour ratings, we can make better decisions when selecting batteries for these applications.

A battery with a high reserve capacity can deliver power for an extended period, reducing the risk of unexpected dead batteries and failures. In critical situations, such as emergencies or power outages, knowing the actual amount of battery reserve capacity can be a lifesaver.

Now let's delve deeper into specific applications where reserve capacity is of utmost importance.

Fishing and Marine Applications

In fishing and marine applications, reserve capacity is crucial because it indicates how long a battery can provide power to the boat's electronics before requiring recharging.

A high reserve capacity battery is essential in these scenarios to ensure extended power for equipment, prevent unexpected dead batteries and reduce the risk of battery failure thus enabling prolonged use without needing recharging or replacing the battery.

By choosing a battery with a high reserve capacity, you can enjoy more time on the water without worrying about power outages or battery issues. This peace of mind is invaluable when navigating the open seas or enjoying a relaxing fishing trip.

SHOP OUR PROCONNECT SERIES LITHIUM BATTERIES FOR MARINE APPLICATIONS

RV Applications

For RV owners, reserve capacity is an equally important consideration. A high reserve capacity battery can provide power for an extended duration, allowing greater flexibility in terms of where the RV can be parked and for how long. 

It also helps to prevent unexpected dead batteries, ensuring that your adventures on the open road remain uninterrupted.

When selecting a battery for your RV, considering the reserve capacity is essential, as it directly impacts the performance and reliability of your vehicle's power system. By choosing a battery with a high reserve capacity, you can enjoy longer trips and greater peace of mind during your travels.

SHOP OUR BAJA SERIES LITHIUM BATTERIES FOR RV APPLICATIONS

Cold Cranking Amps (CCA) and Reserve Capacity

Cold cranking amps (CCA) and battery reserve capacity are two distinct yet essential metrics for evaluating the performance of a battery. CCA measures the current a charged battery can deliver and sustain for 30 seconds at 0°F while still maintaining a voltage of 7.2 volts, essentially determining the battery's ability to start an engine in cold conditions. 

On the other hand, reserve capacity indicates the number of minutes a fully charged battery can deliver power without relying on the vehicle's charging system.

Understanding the differences between these two measurements is important, as they serve different purposes in evaluating battery performance. Cold cranking amps is a short-term measure that determines how long an engine takes to start in a cold environment, while reserve capacity is a long-term measure of how energy is supplied over time.

In cold weather, cold cranking amps becomes a critical factor to ensure that the battery has enough power to start the engine. A battery with a higher CCA rating is more likely to be successful in starting an engine in cold weather than one with a lower rating.

Therefore, when selecting a battery for cold weather, it is advisable to choose one with a higher CCA rating.

This knowledge ensures that your vehicle starts reliably in cold conditions, reducing the risk of being stranded due to a dead battery.

Factors Affecting Reserve Capacity

Several factors can influence the battery reserve capacity, including the type of battery, temperature, age of the battery, usage, charging/discharging rates and the Peukert effect. 

Temperature affects the chemical reactions within the battery, impacting its reserve capacity. Likewise, the age and usage of a battery can influence its reserve capacity due to the effect on the battery's chemical reactions.

And the Peukert Effect basically states that as the rate of discharge increases, the capacity decreases. However, lithium batteries like those we offer, are not impacted by the Peukert effect. 

Understanding these factors is essential when assessing a battery's RC, as they can significantly impact the battery's performance and longevity. 

Shop Now: Check out our great lithium battery options for your power needs. 

How to Determine Your Battery's Reserve Capacity

If the battery reserve capacity is not stated on its label, you can measure its reserve capacity rating by first charging the battery fully. Then remove any surface charge by discharging it briefly with a load. 

Afterward, time how long the battery can deliver a 25-ampere load before reaching 10.5 volts. The duration of this process is the battery's reserve capacity, which should be noted in minutes.

Keep in mind that this method may not be suitable for all battery types and may require specific equipment to perform accurately. Consulting the manufacturer's instructions or seeking professional assistance is recommended to ensure the most accurate measurement of your battery reserve capacity.

Lithium Batteries and Reserve Capacity

As mentioned previously, lithium batteries do have a RC rating, but they usually aren't compared by this feature. This capacity is rarely referred to either. 

Reserve capacity is most commonly associated with lead-acid batteries, which are widely used in vehicle applications, but tend to have lower reserve capacity. It is important to note that reaching the full RC of a lead-acid battery will draw the battery voltage down to 10.5 volts, which is lower than 50% of the charge and can lead to battery failure. 

Therefore, it is advisable to consider reserve capacity more of an upper limit than a target range to avoid dramatically shortening the life of the lead-acid battery.

When comparing lead-acid and lithium batteries, it is essential to understand their respective reserve capacities and how they differ. This knowledge will allow you to make informed decisions when selecting the right battery for your needs. 

However, generally speaking, lithium batteries like those you will find in our lineup will have approximately 40% more battery RC with lithium batteries than lead acid ones. 

Choosing the Right Battery for Your Vehicle

Selecting the appropriate car battery for your vehicle involves understanding the differences between CCA and reserve capacity ratings, as well as considering other factors such as temperature, age, and usage. 

When choosing the right car battery reserve capacity, it is important to consider the battery size, cranking amps, cold cranking amps, warranty, battery type and terminal position.

By considering all these factors and understanding the distinctions between CCA and reserve capacity, you can make educated decisions when selecting a battery for your vehicle. This knowledge will help ensure optimal battery performance and reduce the risk of unexpected battery failures, enhancing the reliability and enjoyment of your vehicle.

Summary

In conclusion, understanding what is reserve capacity on a battery and amp hour rating is crucial for selecting the right battery for your vehicle, RV, or boat. Battery RC provides valuable information about a battery's ability to deliver power over time, while amp hours offer insight into the battery's energy storage capacity. 

By understanding reserve capacity vs amp hours and considering various factors affecting it, you can make informed decisions when selecting batteries for various applications.

We hope that this blog post has provided you with valuable insights and knowledge about reserve capacity, amp hours and battery performance. 

By applying this information, you can ensure that your battery-powered devices and vehicles perform optimally, providing you with peace of mind and confidence in your battery choices.

Frequently Asked Questions

What is a good battery reserve capacity in a battery?

Depending on the battery type, the average RC of a 12V battery ranges from 170-190 minutes for lead-acid batteries and 240 minutes for lithium batteries.

What does 120 reserve capacity mean on a battery?

A battery with a reserve capacity of 120 means it can continuously provide 25 amps of power for up to two hours (120 minutes) before its voltage drops below 10.5 volts.

This makes it an ideal choice for vehicles and devices that require long-term reliability and performance.

How many amp hours is reserve capacity?

Amp hours and reserve capacity do not measure the same thing. A battery reserve capacity is a unit of time, expressed in minutes, describing how long a battery can sustain a 25-amp draw before it reaches 10.5 volts. 

On the other hand, amp hours is the amount of amps that a battery can discharge in one hour. 

How do you calculate battery reserve capacity?

Battery reserve capacity is calculated by dividing the amp hours by 25, and then multiplying that number by 60. It's important to remember that this number is not an indicator of energy, as voltage is not factored in.

The two are related by the following equations: 

• Ah = (RC / 60) x 25
• RC = (Ah / 25) x 60

NEED MORE ASSISTANCE PLANNING YOUR POWER SETUP?  GIVE US A CALL AT 303-968-1366 AND OUR TEAM WILL HELP YOU GET STARTED!