Battery and low-power glossary

Burden voltage is the voltage drop that occurs in the current measurement instrument that has a shunt resistor in series with the device under test (DUT) while measuring the current. Burden voltage affects the measurement, leading to inaccuracies, especially in low-voltage, low-power applications.

Otii Arc Pro and Otii Ace Pro actively regulate voltage, eliminating burden voltage for reliable and precise low-power measurement.

In isolated power supplies, the input and the output sides are electrically separated using transformers or optocouplers. Isolated power supplies add an extra layer of safety, avoid ground loops, and enable series connection with another power supply.

Otii Ace Pro is an isolated power supply. More about smart power supplies, read here.

Wide dynamic range refers to a system’s ability to accurately measure or process signals spanning a large range of values, from very small to very large, without compromising the precision. In the context of low-power measurements, it refers to the ability to accurately measure from nanoamperes (nA) to amperes (A) without losing detail when profiling sleep, standby, and active states in embedded electronics.

In-line (Ampere Mode) power measurement: the measurement device is connected in series with the device under test to measure the current flowing through the system. Named after the ampere, which it primarily measures.

Most instruments provide either full-power-mode measurements or only ampere-mode measurements. Otii Ace Pro provides both options. Furthermore, to measure additional voltage, power, and energy, the ampere-mode setup can be extended with a 4-wire connection via SENSE pins in the Ace’s expansion ports. See application note. 

A programmable load is an electronic test device that simulates different load conditions by dynamically adjusting voltage, current, resistance, or power. It actively and in real-time changes the load characteristics, enabling testing of a power source (battery, power supply, PV cell) behaviour for different usage conditions.

It draws energy from the power source and can allow for the control over:

• Constant Current (CC) – The load maintains a fixed current regardless of voltage.
• Constant Voltage (CV) – The load maintains a fixed voltage regardless of current.
• Constant Resistance (CR) – The load simulates a specific resistance value.
• Constant Power (CP) – The load dynamically adjusts resistance to maintain a fixed power level

A programmable load is used in battery testing, battery profiling and emulation, power supply validation, and electronics design.

Otii Arc and Otii Ace become programmable loads with Otii Battery Toolbox.

Low-power measurements aren’t about how small a value you can detect — they’re about how accurately you can measure those small values. Accuracy is specified as ±(gain error + offset error), or ±(X% + Y), where X is the percentage error, and Y is the offset error. This means your measurement includes both a fixed offset error in Y and a scaling error of X%.

Example: the current measurement accuracy for the main channel of the Otii Ace when measuring low currents is ±(0.05% + 25nA). So if you measure 1 µA, the expected error would be a maximum of 0.0255 µA. Check out a technical article on the topic.

When measuring currents and voltage with thin, long cables the resistance in the cables and connectors might cause errors in the voltage measurement. In a 2-wire setup, current and voltage share the same path, and resistance can affect the accuracy. A 4-wire setup uses separate wires for power and voltage sensing, thereby avoiding the additional error introduced by cables and connectors.

4-wire measurements can be used in any setup with Otii Arc and Ace Pro.

A power profile represents how an electronic device consumes energy over time across different operational states, such as sleep, wake-up, sensor reading, data processing, and transmission. It provides visibility into current, voltage, and power variations, helping identify unexpected behaviour and spikes, and how frequently they occur.

With Otii Ace Pro and Arc Pro, you can measure highly accurate power profiles for embedded systems operating up to 25V/5A, fully synchronized with UART and GPIO traces, all at the same time.

Power Saving Mode is a low-power idle state in LTE-M and NB-IoT that allows the device to sleep for extended periods while remaining registered to the network. It is a feature defined in 3GPP standards for LTE-based cellular IoT.

Otii Arc and Ace Pro support AT commands to configure the device for PSM mode and accurately measure ultra-low currents down to the nanoampere level. Check out a technical article on the topic.

AT commands are text-based instructions used to configure and control communication modules (e.g., cellular, Bluetooth, GNSS). In low-power IoT design, AT commands are commonly used to manage radio behavior, trigger power-saving modes (e.g., PSM, eDRX), and reduce energy consumption.

Otii Arc and Ace Pro support AT commands, which can be sent directly from the UART log window in the Otii app – making low-power testing, tuning, and optimization smooth and time-efficient. See application note.

Continuous Integration (CI) is a core software development practice where developers frequently merge their code changes into a shared repository, and each change is automatically built and tested. Continuous Integration (CI) with power or energy measurements is an automated, data-driven validation of energy efficiency at every code change. It is practiced to:

• Detect power regressions early – e.g., a firmware change that increases current draw.
• Quantify efficiency impact per commit – see how code affects real-world energy use.
• Track trends over time – build a power-performance history across versions.
• Automate ROI analysis – for energy optimizations or component changes.

Otii Arc/Ace can easily integrate into any CI flow using the Otii Automation toolbox. See application note.

Ampere-hours (Ah) and watt-hours (Wh) are both units of battery capacity, but they represent different aspects. Ah measures the charge capacity, indicating how much current a battery can deliver over time, while Wh measures the energy capacity, indicating how much total energy the battery can store. The key difference lies in voltage: Ah is useful for comparing batteries at the same voltage, but Wh is more accurate for comparing batteries at different voltages. 

Check out a technical article on the topic.

Battery discharge profiles describe how a battery’s voltage changes over time (or over capacity) as it discharges under a load. They’re crucial for understanding battery performance and are typically presented in battery data sheets as a plot of Voltage (y-axis) vs. Time (x-axis) or Capacity (y-axis) vs. Time (x-axis). The load is typically assumed constant. Pulsed loads better reflect the real-world conditions batteries face in sensor and IoT devices.

If you are discharging batteries with Otii Arc, Ace Pro, and Otii Battery Toolbox, your battery discharge profiles for pulsed loads will include internal resistance information and can therefore be used to emulate battery behaviour. See application note. 

Internal resistance is the opposition to current flow within a battery, caused by its materials, chemical processes, and structure. It causes voltage drops and heat generation under load and typically increases with battery aging, temperature changes, and usage, thereby affecting overall performance and efficiency.

If you are discharging batteries with Otii Arc, Ace Pro, and Otii Battery Toolbox, your battery discharge profiles for pulsed loads will include internal resistance information and can therefore be used to emulate battery behaviour.

A primary battery is a non-rechargeable battery designed for single-use. It is expected to offer high energy density, long shelf life, and low self-discharge, making it ideal for low-power, long-lived applications such as IoT sensors, remote controls, and medical devices. The most common chemistries are alkaline, lithium, and zinc-carbon.

Otii Product Suite offers set-ups for battery profiling, validation, and testing to help you choose the right battery for your application.

A secondary battery is a rechargeable battery that can be discharged and recharged multiple times. Common chemistries include lithium-ion (Li-ion), nickel-metal hydride (NiMH), and lithium iron phosphate (LiFePO₄). Used in applications that require frequent energy cycling; ideal for wearables, smartphones, electric vehicles, and some IoT devices with energy harvesting or access to charging.

Otii Product Suite offers set-ups for battery profiling and cycling of the secondary batteries to help you validate your choice.

State of Health (SoH) is a metric that reflects a battery’s overall condition relative to its new state. It typically indicates how much of the battery’s original capacity, power delivery, or performance it can still provide.

SoH is influenced by several factors, including the number of charge/discharge cycles, exposure to extreme temperatures, storage conditions, and natural aging. A lower SoH means the battery stores less energy or delivers less power than it originally could—even if it is fully charged.

Because SoH tracks long-term degradation, it is primarily used for rechargeable batteries, where monitoring health over time is essential.

SoH is often confused with State of Charge (SoC), but they refer to different characteristics:

• SoC indicates how much charge is currently available — applicable to both rechargeable and non-rechargeable batteries.
• SoH indicates how much of the battery’s original performance remains — mainly relevant for rechargeable batteries.

Battery self-discharge refers to the gradual loss of charge that occurs in a battery even when it’s not connected to any device or load. This is an unavoidable effect caused by internal chemical reactions. The rate of self-discharge depends on both the battery type and chemistry, as well as the temperature at which it is stored or operated. For example, some battery types—such as lithium-ion—can lose up to 30% of their charge in a month when exposed to tropical temperatures.

When estimating battery life with the Otii Battery Life Estimator, you can include the battery’s self-discharge rate, either measured or sourced from the datasheet, to improve accuracy.

State of Charge (SoC) is the ratio of the current charge in a battery to its maximum charge capacity, expressed as a percentage (SoC = (current capacity / maximum capacity) × 100%). Accurate SoC estimation, based on techniques such as open-circuit voltage measurement, Coulomb counting, or model-based algorithms, is critical for battery management systems (BMS) to optimize performance, ensure safety, and extend battery lifespan.

Using Otii Ace/Arc Pro and Otii Battery Toolbox, you can emulate batteries for different SoCs for your embedded device and specific use case.

Battery cycling is a method of repeatedly charging and discharging a battery to evaluate its energy loss over time, assess its energy efficiency (by comparing energy input to output), and determine how many cycles it can withstand before it begins to degrade.

The Otii Ace Pro and Otii Battery Toolbox can be utilized for battery cycling to achieve these objectives. They offer customizable settings to simulate real-world usage in a controlled environment. See application note.

Battery aging is the gradual deterioration of a battery’s capacity and performance over time due to chemical and physical changes within the cell. It results in reduced energy storage, higher internal resistance, and a shorter operational life, and is influenced by factors such as temperature, charge cycles, state of charge, and storage conditions.

Otii Ace/Arc Pro and Otii Battery Toolbox offer battery cycling to test aging and feature a fully customizable test sequence, unlimited test cycles, multi-battery support, and a clean, intuitive user interface. See application note.

Incoming inspection is the process of verifying components or materials as they arrive from suppliers to ensure they meet the specified requirements. In battery and power applications, this means verifying the quality and consistency of cells, capacitors, or PV modules before use.

Otii Battery Validation, together with Otii Ace Pro, is commonly used during incoming inspections to verify the quality and performance of batteries, PV cells, and supercapacitors.

Passivation in lithium batteries with liquid cathodes (like Li-SOCl₂ and Li-SO₂Cl₂) forms a protective lithium chloride (LiCl) layer on the anode, preventing internal short circuits and enabling long shelf life. However, this insulating layer increases internal resistance, causing a startup-voltage delay that worsens over time during storage.

Using Otii Ace Pro and Otii Battery Toolbox, developers can measure the effects of battery passivation and more accurately predict their products’ battery life. See application note.

A supercapacitor is an energy storage device that stores charge electrostatically, enabling rapid charge-discharge cycles with high power density. Unlike batteries, supercapacitors have low energy density but extremely low internal resistance (ESR), making them ideal for handling short, high-current pulses and stabilizing voltage during load transients.

In hybrid power architectures, supercapacitors are often used in parallel with primary cells (e.g., Li-SOCl₂) to absorb peak loads and minimize voltage drops.

Using Otii Ace Pro with a 4-wire measurement setup, you can analyze supercapacitor behavior by tracking storage efficiency and performance under deep voltage drops and repeated pulses. Check out a technical article and benchmark on the topic. 

Electric Double-Layer Capacitor (EDLC) is a supercapacitor that stores energy electrostatically rather than chemically. When a voltage is applied, electric charge accumulates at the interface between an electrode and an electrolyte, forming two thin layers of opposite charge – called an electric double layer. EDLCs are forgiving by design: they operate across a wide temperature range, have no strict minimum voltage, and discharge in a predictable, linear way.

Use Otii Ace Pro together with the Otii Battery Toolbox to characterize EDLC supercapacitor behavior during system integration.

Coulomb counting is a method for tracking charge flowing into and out of a battery and integrating current over time (ampere-seconds) to estimate its State of Charge (SoC). It is often combined with voltage-based methods for higher accuracy. While simple voltage monitors are typically built into most MCUs or PMICs, Coulomb counter ICs are usually separate components that require additional energy, board space, calibration, and incur extra cost. As a result, they are primarily used in mission-critical applications.

A photovoltaic (PV) cell, also known as a solar cell, converts light into electrical energy using the photovoltaic effect. The output characteristics, open-circuit voltage (Voc), short-circuit current (Isc), and maximum power point (MPP), are strongly influenced by irradiance, temperature, and the underlying PV cell technology.

With the Otii Ace Pro, you can characterize a PV cell, measure the energy it provides, and assess how well it aligns with your device’s power requirements. See application note. 

An IV curve (current-voltage curve) characterizes the electrical behavior of a photovoltaic (PV) cell by plotting output current (I) versus voltage (V) under specific illumination and temperature conditions. Providing key parameters such as open-circuit voltage (Voc), short-circuit current (Isc), and maximum power point (MPP), critical for designing and validating energy-harvesting embedded systems.

Using Otii Ace Pro, you can measure and create IV curves for PV cell validation and quality assurance.

Maximum Power Point Tracking (MPPT) is a method used in photovoltaic (PV) systems to continuously adjust the operating point of a PV cell to maximize power under given light and temperature conditions. Since PV output varies with illumination and load, MPPT maximizes harvested energy. It is typically a Power Management IC (PMIC) that uses this technique, but it can also be a DC/DC converter or a dedicated MPPT controller within an energy-harvesting circuit.

With Otii Ace Pro, you can gain detailed insights into how the MPPT of your PMIC operates. Check out a technical article on the topic.