Reading a Battery Datasheet
Every technological product has a list of technical specifications that follow industry standards to ensure uniformity across different manufacturers.
When you window shop for a laptop, more often than not, you start by looking at the list shown in Fig 1. Once satisfied with the specifications, you move to other parameters like aesthetics and portability before hitting the “Buy” button.
Similarly, a battery has its own list of technical specifications that is made available by the manufacturer in the form of a datasheet. In fact, every electronic/electrical component viz. resistor, capacitor, inductor, processor has a datasheet which is provided by the manufacturer. The best part is that datasheets are freely available for download. While the first appearance of a datasheet may look overwhelming and nerdy (like in Fig 2),
Pre-requisite — I strongly recommend reading Pick the Best: Metrics to Select Batteries for basic terms and definitions used to characterize a battery.
in reality, it does the job of a restaurant’s menu card (Fig 3) by answering “What to expect from the restaurant?”.
Note — The image of the menu card is only used for educational purposes and not for promotion.
Similarly, a battery datasheet is a “sheet” consisting of all the necessary “data” regarding the battery. The experience of reading a datasheet for the first time is like an information overdose. Hence, knowing which parts to read is crucial.
This article analyses various sections of a typical datasheet with the help of an example — lithium-ion battery, iR18650 having a capacity of 2600 mAh. This datasheet is provided by EEMB Co. Ltd and can be found here.
Battery Datasheet : Sections
Caution — Necessary precautions to be taken when using and discarding the battery (Fig 4).
Battery and Electrical Characteristics — Describes deliverables of the battery.
Customers often use these characteristics to compare and make informed decisions. In fact, 99% of the required information is available in these two sections and the rest can be conveniently skipped. For instance, in general purpose use cases (daily-life activities), users (like you and me) would be contented with the following:
- Capacity (5.1 in Fig 5)
- Nominal Voltage (5.2 in Fig 5)
- Standard Discharge Current (5.8 in Fig 5)
- Operating Temperature (5.13 in Fig 5)
- Capacity Retention (8.13 in Fig 6)
- Cycle life (8.14 in Fig 6)
Plots — The datasheet also presents with suitable plots to better understand the characteristics. Fig 7 shows four plots depicting the variations in battery characteristics.
- Rate Discharge Characteristics Plot — Decrease in the nominal voltage of LIR18650 depends on the discharge capacity or C-rate. The decrease is higher for higher C-rates (magenta line has the highest C-rate — 3C).
- Charge Characteristics Plot — Red and blue lines indicate the time taken for nominal voltage and capacity to reach their desired values as LIR18650 is being charged. As the battery charges, the amount of current it accepts decreases and is indicated by the green line.
- Discharge Temperature Characteristics Plot — Depicts the battery performance at borderline temperatures — a maximum temperature of 55 °C and a minimum temperature of -20 °C. The graph describes how quickly the battery discharges when exposed to the prescribed minimum and maximum temperatures.
- Cycle Characteristics Plot- Indicates the battery’s performance with respect to the number of charge-discharge cycles over time. As expected, the performance decreases over time because of external factors beyond one’s control — accidental subjection to borderline operating temperatures or natural decrement due to continuous usage.
The next sections are best suited for application-specific demands which require precision and durability. Under such circumstances, operating the battery safely becomes an equally major concern.
Safety Performance — The “items” column in Fig 8 lists possible perilous phenomena. The battery is deemed “safe” if it satisfies the condition — “No fire, no explosion” for each of the mentioned phenomena.
A safe battery does not cause an explosion or lead to a fire when short circuited. The procedure to short circuit the battery is mentioned in the “Test Procedure” column.
Environment Tests — Similar to safety tests, these are tests performed to determine whether the battery functions as expected under the so called usual operation conditions.
If a manufactured unit does not have a capacity greater than 2080 mAh at high temperatures, it is set aside and adjudged faulty.
Hopefully, this post provides a headstart and removes initial barriers to reading and understanding any datasheet (irrespective of the product). I strongly believe that reading a datasheet is an art and requires patience like any other skill. However, learning the art is worth the effort as you gain insights into nuances of the product’s functionality.
Thank you everyone for your time.
References
[1] Dell, “Dell XPS 9380”, Amazon.in
[2] Texas Instruments. “uA741 General Purpose Operational Amplifiers”, Nov, 1970 Revised — Jan, 2018
