Need-to-know battery technical terms in plain English
Being able to understand the battery information or technical specifications you see on our website should not be overwhelming or require you to learn a lot of techspeak. In this post, we explore just a handful of the most common battery terms you are likely to encounter, taking care not to take you deep diving into the heavy scientific concepts attached to them. Most of you can clearly get the basic gist in the quick definition of each term. The expanded sections serve to provide clarity or additional details.
Capacity: For example, “This higher capacity battery will allow you to work longer.”
Quick definition: All that we are talking about here is how much of its energy a battery can deliver over time. It is often expressed as Ah (ampere hours) or mAh (milliampere hours). A 100 Ah battery can be depleted of its power at a rate of 100 amps in one hour, or 50 amps over a 2-hour period, or 25 amps over a 4-hour period, and so forth.
Extended: The higher a battery’s capacity rating, the longer will be its runtime. If you require a lithium battery at a specific voltage, ideally, you should not deviate from this. However, you can install a battery with a higher Ah or mAh than your current battery to extend your device’s run time; or conversely, you can put a lower capacity Ah or mAh-rated battery to decrease runtime. (It is important to distinguish if the capacity ratings are shown in Ah or mAh. For those on the imperial rather than the metric system, there are 1,000 milliamps to every 1 amp. So, a 2,400 mAh battery can be described as 2.4 Ah battery.)
C-Rate or C-Rating: (Please refer to extended section of ‘Maximum Discharge Rate’ further below.)
Drain: For example, “This battery is suitable for high drain devices.”
Quick definition: This simply refers to the extent at which your battery is depleted of its power, or that a device consumes your battery’s power. High drain would mean quickly; low drain denotes the opposite.
Extended: Depleting a battery’s power means we are draining its voltage, which is its energy. The term is often used to describe the device relative to the battery. So, a high drain battery is suitable for devices that quickly consume power. Low drain describes the polar opposite. A low drain battery, for example, would not be suitable for a high drain device that requires adequate power to efficiently operate. A car or a drill is a high drain device. A clock is a low drain device.
Energy density: For example, “Lead acid cells generally have a low energy density.”
Quick definition: This is how much energy (i.e., volts, or power) a battery stores relative to its size.
Extended: Energy density is often used in relative terms. Take, for example, a comparison between an AA lithium battery and an AA alkaline battery. The lithium battery packs a much higher energy density at 3.6 – 3.7 volts than its identically-sized alkaline counterpart rated at 1.5 volts. Another way to look at it: consider the physical size of the lithium AA battery at 3.7 volts compared to lead acid car battery that is physically tens of times larger and heavier, rated at 12.6 volts. Clearly the lithium AA has a much higher energy density in proportion to its size. You know that expression, pound for pound this one packs more punch? That is basically what we are talking about here.
Maximum discharge rate: For example, “The battery’s maximum discharge rate is 2C.”
Quick definition: This simply refers to the maximum current at which a battery can be discharged continuously without overheating or destroying it. Battery manufacturers often define this in terms of C-Rate (described in the next paragraph) to prevent excessive discharge rates that would otherwise damage the battery or reduce its capacity.
Extended: A technical explanation is unavoidable here, but let’s try to simplify. A C-Rate measures the rate at which a battery is discharged relative to its maximum capacity. At its most basic, a C -Rate of 1 means that the discharge current will deplete your battery in 1 hour. Taking it a notch further, if your battery’s capacity is 3 Ah, but has a C-Rate of 2, you can actually choose to discharge the entire battery at 6 Ah, or double its rated capacity; but, doing so repetitively or for extended periods will expectedly reduce your battery life. On a final note, C-Rate is inversely proportional to your battery’s capacity, so as you move up in capacity, you can move down your C-Rate.
Self-discharge: For example, “Ni-MH batteries self-discharge at a faster rate than lithium batteries.”
Quick definition: This is the battery’s loss of power over time while not being used. It is usually expressed as a percentage relative to a month or a year. A lower figure is generally preferred.
Extended: The key word is ‘self’. The battery is self-depleting its power in storage doing nothing as opposed to losing its power to a device consuming it. All batteries suffer from self-discharge in varying degrees. Nickel-based rechargeable batteries, such as the Ni-MH battery can self-discharge as much as 20 – 30 percent of their power in just one month of inactivity. A stored lead-acid battery might self-discharge at a rate of 5 – 15 percent in the same amount of time. A lithium battery offers among the lowest self-discharge rates—as low as 2 percent per month. A lower self-discharge rate is generally preferred as this contributes to a higher shelf life (below).
Shelf life: For example, “This battery model has an expected shelf life of up to eight years.”
Quick definition: This term is closely related to ‘self-discharge’ (above). It describes in months or years how long the battery is fit for consumption even as it is idly stored. All batteries slowly lose their charge as soon as they are manufactured and continue to do so over time. As expected, a higher shelf-life is generally preferred.
Extended: Battery shelf life varies and is largely based on the self-discharge rate inherent to its chemistry.
State of Charge (SoC): For example, “Store the battery at least forty percent state of charge.”
This is simply an expression of the battery’s current charge state relative to its maximum (or 100 percent) charge capacity. It is normally expressed a percentage. That’s it.
Temperature Range: For example, “Ni-MH battery temperature ranges are generally 0° ~50° C, -20° ~30° C, 0° ~50° C.”
Quick definition: The temperatures at which a battery is able to optimally supply power at different states, for example, when discharged, stored, and charged.
Extended: A battery should be able to supply power in the specified discharge temperature range, degrade slowly in the storage range, and maintain capacity in the charged temperature range if charged. Usage outside of the temperature ranges will vary by battery chemistry.
Voltage and voltage range and voltage curve: For example, “A 3.6-volt lithium battery generally has a flat voltage curve and a voltage range of 2.8V-3.6V-4.2V.”
Quick definition. It is not as complicated as it sounds. Voltage is the available power or energy of a battery. The way that a battery’s power is available over the course of its service life is specific to its chemistry and is graphically depicted or stated as a voltage curve. Since available voltage when a battery is nearly depleted is not the same as when the battery is fully charged, voltage range simply states the minimum to maximum voltage capability.
Extended: Voltage range is often expressed as minimum-nominal-maximum. In the example, “2.8V-3.6V-4.2V,” The middle, or nominal, value is often the referenced rated voltage on the battery itself. At the minimum value, which in this example is 2.8V, the battery can be considered dead or depleted. At maximum value, specified in the example as 4.2V, it is fully charged. The voltage curve shows how the battery maintains voltage over its lifespan. For example, alkaline continuously depletes its power over time, which can be represented by a gradual downward sloped curve and described as ‘curved’. A silver oxide watch battery, on the other hand, will maintain a steady flat line—or the same power—over the course of it service life, before steeply dropping in its final hours. It is, therefore, described as ‘flat’.
Further reading:
Making sense of battery certification symbols
Understand the relevance of various markings imprinted on batteries.
ANSI and IEC battery standardization nomenclature
Review basic IEC and ANSA nomenclature that can help you determine battery interchangeability when shopping for replacements.
