Battery Reserve Capacity

There are many aspects to consider when choosing the most appropriate battery as a source of redundant energy. This is particularly relevant in terms of off grid power systems that rely upon batteries in the event that mains electricity fails. One variable that needs to be addressed is known as battery reserve capacity. We will take a closer look at this concept as well as its ramifications immediately below.

Battery Reserve Capacity: An Overview

Sometimes referred to by the acronym "RC", battery reserve capacity is defined as the amount of time that a cell is capable of functioning before falling below a specific output threshold. This is measured in the form of "reserve minutes".[1]

It is important to note the difference between battery reserve capacity and other common measurements such as ampere hours (Ah). Ampere hours indicate how many amps a battery can provide over a period of one hour. On the contrary, battery reserve capacity is instead concerned with the amount of time that a battery will last before becoming depleted. An example will help to reinforce this point:[2]

The capacity of a typical 12-volt car battery is measured in relation to how long it can provide 25 amperes before falling below 10.5 volts. Assuming that this equates to one hour and 30 minutes, the associated battery reserve capacity would be 150. As we can see, battery reserve capacity is always measured in terms of minutes.

While this might appear slightly complicated at first glance, modern technology now allows consumers to access online battery reserve capacity calculators. Users can simply input specific information into discrete fields. These calculators will then automatically determine how many ampere hours are remaining before the cell in question drops below a certain threshold. In terms of the battery reserve capacity of a typical car battery, this would once again refer to 10.5 volts.[3]

Why is Reserve Capacity Important?

Battery reserve capacity is much more than a theoretical measurement alone. Let us once again refer back to a standard motor vehicle. In this sense, battery reserve capacity would be used to calculate how long a fully charged battery will continue to operate in the event that the alternator fails.[4] Assuming that a long journey is being planned or that the vehicle is used for emergency services, its battery reserve capacity suddenly takes on an important role. Furthermore, determining battery reserve capacity can be a pivotal factor when analysing different brands and their intended uses.

What is Considered an Adequate Reserve Capacity?

So, what is typically referred to as a "good" or "adequate" battery reserve capacity? While definitions will slightly differ, most industry professionals feel that a battery should be able to supply at least 25 amperes of power before the voltage starts to drop[5]. Once again, this is measured in the amount of minutes that continuous power can be supplied. Batteries that are not able to offer this level of reliability are often considered low-quality products.

Battery Reserve Capacity Differences Between Lead Acid and Lithium Cells

Is there any difference between lead acid batteries and lithium-ion batteries in terms of their battery reserve capacities? In this sense, efficiency is entirely relevant. A typical 12-volt 100Ah lead acid battery will normally supply between 170 and 190 minutes of power. A lithium-ion battery is rated slightly higher; generally offering a reserve of 240 minutes before its reserves fall below 10.5 volts.[6]

Lithium cells are therefore preferred within networks that might require an off-grid source of power for extended periods of time. Real-time measurement technology (such as SCADA systems within the oil and gas sector) represent an instance when lithium-ion batteries can have a very real impact upon both efficiency and reliability.

The Future of Battery Reserve Capacity

While it is clear that the battery reserve capacity of lithium-ion cells is greater than that of a typical lead-acid unit, hydrogen fuel cells could further transform the entire sector. Fuel cells as power generators are very efficient while weighing significantly less. These are some of the reasons why the EFOY Fuel Cells have become popular within many sectors.

Although the notion of battery reserve capacity might be unfamiliar to many consumers, the fact of the matter is that this critical metric can never be taken for granted when determining which unit offers the greatest level of on-demand reliability.