Battery Safety Guide

ย When we talk about safety one of the first questions to answer is, what is the difference between a Cell and a Battery?

A cell and a battery are both electrochemical devices that convert chemical energy into electrical energy. However, there is a distinction between the two terms.

Cell: A cell is a single unit that generates electrical energy through an electrochemical reaction. It consists of three main components: two electrodes (a positive electrode called the cathode and a negative electrode called the anode) and an electrolyte that allows ions to move between the electrodes. When a chemical reaction occurs between the electrodes and the electrolyte, it generates a potential difference (voltage) between the electrodes, resulting in the flow of electric current. A single cell can be used as a power source for smaller devices, but its voltage output is typically limited.

Group of batteries
A group of cells.

Battery: A battery, on the other hand, is a collection of multiple cells connected together in a specific arrangement. The purpose of connecting cells in a battery is to increase the total voltage and capacity available. Batteries are designed to provide a more reliable and sustained source of electrical energy for various applications, ranging from small devices like remote controls to larger devices like laptops, smartphones, vehicles, and even power grids. By combining multiple cells, batteries can deliver higher voltages and store more energy.

Lithium battery repair, a DeWalt power tool battery like this will consist of cells and a BMS
A Battery made up from a group of cells.

In summary, a cell is a basic unit that generates electrical energy, whereas a battery is a combination of multiple cells arranged to provide higher voltage and capacity.

Cells are typically ‘unprotected’ which means they require a device to manage them, in terms of discharging, charging and detecting faults etc. A BMS (Battery Management System) is what is used to do this.

A Battery Management System (BMS) is an electronic control system designed to monitor and manage the various aspects of a rechargeable battery pack. It plays a crucial role in ensuring the safe and efficient operation of batteries, especially in applications where multiple battery cells are connected in series or parallel to form a larger battery pack.

The main functions of a Battery Management System include:

  1. Cell Monitoring: A BMS monitors the voltage, current, and temperature of individual battery cells within a battery pack. This information helps ensure that all cells are operating within safe limits and helps detect any cells that might be performing poorly or deviating from the norm.

  2. Balancing: In a battery pack, individual cells may have slight variations in their capacity or voltage characteristics. Over time, these variations can lead to imbalances, affecting the overall performance and lifespan of the pack. A BMS can implement cell balancing by redistributing charge among the cells to maintain uniformity and prevent overcharging or over-discharging of any individual cell.

  3. State of Charge (SoC) Estimation: The BMS calculates and estimates the remaining energy or charge in the battery pack, commonly referred to as the State of Charge (SoC). This information helps users understand how much energy is left in the battery and plan accordingly.

  4. Overcharge and Overdischarge Protection: The BMS prevents cells from being overcharged or over-discharged, both of which can be dangerous and can significantly reduce the battery’s lifespan. The BMS will disconnect the charging source or load if a cell’s voltage exceeds safe limits or drops too low.

  5. Temperature Management: Lithium-ion batteries, in particular, are sensitive to temperature changes. A BMS monitors the temperature of each cell and the overall pack, and it may take actions such as reducing charging or discharging rates if temperatures become too high to prevent damage.

  6. Communication and Reporting: Some advanced BMS systems offer communication interfaces, such as CAN (Controller Area Network) or UART (Universal Asynchronous Receiver-Transmitter), allowing the system to communicate with external devices like controllers, displays, or monitoring systems. This enables real-time data exchange and remote monitoring.

  7. Fault Detection and Alarms: If any critical faults or anomalies are detected, such as excessive voltage, temperature, or current, the BMS will trigger alarms or shutdown procedures to prevent further damage.

Battery Management Systems are commonly used in various applications, including electric vehicles, renewable energy systems (like solar and wind power storage), industrial equipment, consumer electronics, and more. They are essential for optimizing the performance, safety, and lifespan of battery packs, which can be complex and potentially hazardous systems to manage without proper control mechanisms.

The dangers of cells & batteries

When we talk about cells vs batteries, the risks are similar but still different.

Thermal Runaway and Fire Risk: Lithium batteries and lithium cells can experience thermal runaway, a process in which the internal temperature of the cell increases uncontrollably due to chemical reactions. This can lead to the release of gas, swelling, rupture, and even explosion of the cell. Thermal runaway can also cause fires that are difficult to manage. 

With cells, this can be down to poor-quality cells, storage conditions, physical damage, or contamination that short circuits the cells (connects the positive directly to the negative). 
With batteries, this can be down to all of the above but we also have the failure of the BMS to consider too. 

A BMS fault is by far the largest cause of thermal runaway, with physical damage being the next likely.

Overcharging and Overheating: Overcharging a lithium cell/battery or subjecting it to high temperatures can lead to thermal runaway. Overcharging can cause the cell’s components to break down, release gas, and potentially ignite. High temperatures can destabilise the cell’s chemistry and increase the risk of failure.

Cells can’t charge themselves, so it doesn’t affect them. Most BMS and chargers have overcharge and overheat protection, so again, it comes down to the quality charger or BMS you are using.

Physical Damage: Lithium cells are sensitive to physical damage. Any punctures, crushes, or impacts can damage the internal structure of the cell, resulting in short circuits, overheating, and potential fires.

Equally true of cells and batteries, you need to treat them carefully.

Counterfeit and Poor-Quality Cells: Low-quality or counterfeit lithium cells and batteries may lack proper safety mechanisms, increasing the risk of thermal runaway, overheating, and fires.

While we all like to save a few dollars, choosing generic cells/batteries and chargers can be likened to playing roulette!

Aging and Storage: Lithium batteries and the cells inside them can degrade over time, especially if stored in extreme temperatures or at full charge. Degraded cells are more prone to failures and thermal events.

Again you need to treat these devices with respect; they carry a lot of power. 

To mitigate the risks associated with lithium batteries, manufacturers incorporate safety features into the BMS, such as overcharge protection, temperature sensors, and pressure relief mechanisms into their designs.

However, users should follow proper charging practices, avoid exposing cells to extreme temperatures, prevent physical damage, and choose reputable products from reliable sources.

While the potential dangers of lithium cells are real, they can be managed with careful handling and usage. Adhering to manufacturer guidelines and employing good practices can help reduce these risks and allow you to use lithium cell-based devices safely.

We hope you’ve found this guide useful.