Every device requires unique power and energy needs, whether it requires a strong jolt of power when starting up or a steady amount of energy for long periods of work activity. Yet factors such as aging, degradation, extreme temperatures, and severe discharging events can impact the available capacity of a battery cell.
When designing custom battery packs, customers must also take into consideration the long-term reliability of a battery pack.
Determining the Right Cell Selection
Careful evaluation of the application, charging requirements, space availability, and environment allows you to determine the type of cell chemistry and format. If the environment experiences extreme temperature fluctuations, you want certain cell chemistries that will operate optimally in those circumstances. For example, cell chemistries such as lithium operate better in low-temperature environments versus lead acid. However, they charge much more slowly in cold environments.
Figure out the type of battery chemistry that will provide the appropriate energy and power. Then narrow down your choices based on the environment. In cases where battery cells will require extra protection from moisture, heat, cold, or vibration, enclosure redesign may provide additional mechanical protection. Insulated cells can ward off moisture while providing stability from vibrations and shocks. To control temperatures and off-gassing with the working batteries, venting, heaters, and fans will keep cells at the right safety range.
Space availability is also a factor in long-term longevity. Some applications will have limited space, which will impact the amount of cell capacity, voltage, and current. Cell format and configuration can overcome these obstacles. Cylindrical, prismatic, and pouch cell formats can provide energy density while accommodating varying space requirements. Certain cell configurations can create varying voltage and run-time increases. Placing batteries in a series will provide an increase in available voltage, while a parallel configuration offers a higher amp hour while maintaining the same voltage.
Prismatic battery cells during assembly process.
Seeking Conservative Working Voltage Window and DoD
Conservative working voltage window and depth of discharge (DoD) are measurements used to set operational limits. Both are designed to lengthen the battery's life, minimize stress, and reduce degradation. The conservative working voltage window is a voltage range that allows the battery cell to provide power without exceeding the established limits.
If a battery voltage is 4.2 volts for charging and has a discharge rate of 3.5 volts, the cell should not reach the maximum state. Instead, the conservative working voltage window state would stay from 3.5 volts to 4 volts. Keeping the voltage in this range improves the operational safety of the battery while lowering degradation caused by overcharging.
The depth of discharge measures how much of the battery's total capacity has been used by the device. The DoD is percentage-based. So, if a battery's amp-hours are 100Ah and it discharges to 30Ah, the DoD measurement would be 30%. When considering the long-term reliability of the battery, you should seek to reach the most conservative DoD before having to recharge the battery. This aspect lengthens the run-time of the battery by efficiently increasing the number of charging and discharging cycles. Instead of completely draining the battery by 90% for 9,000 cycles, the conservative DoD would allow the battery to be discharged at 20% would provide an extra 3,000 cycles to the cell's lifespan.
Selecting Thermal Management and BMS Options
Heat buildup creates a negative working environment for a battery pack. In addition to dealing with exterior heat from the environment, the cells themselves generate heat during operation and when charging. Thermal management options for battery cells include proper heat dissipation techniques. Providing spacing between each cell allows for air flow and lowers the chances of thermal runaway. Additional options include the use of heat sinks, PCM, and insulation for heat transfer capabilities. Air cooling and liquid cooling methods may also transfer heat away from the cells and dissipate it through the battery pack enclosure.
Determining the temperature of the battery requires the right selection of a battery management system (BMS). The BMS consists of sensors and controls that can automatically signal a temperature issue to the user as well as control heating/cooling components to bring the internal temperatures back to a safe range. Additionally, the BMS also monitors other aspects of the battery, including the voltage and current. By monitoring the state of charge (SoC) and state of health (SoH), the system prevents the battery from overcharging, over-discharging, and overheating.
Also consider obtaining a BMS that provides cell balancing. Cell balancing ensures that each cell has the same voltage throughout the battery pack. When the cells are unbalanced, one cell will have a lower or higher charge than the rest. This problem can shorten the lifespan of the battery and increase the chances of overcharging or over-discharging. Unbalanced cells also lead to degradation of weaker cells, which leads to a loss of capacity.
Summary
Battery cells can experience varying operational issues that can impact their life cycle. Understanding the power and energy needs of the device allows you to select the right cell chemistry, format, and configuration inside the enclosure. Then you can include thermal management, BMS, and enclosure options that are suitable based on the environment and daily usage. These options will increase the number of charging and discharging cycles while minimizing capacity loss.
Key Takeaways
- Proper cell selection drives long-term reliability: Choosing the right cell chemistry and format based on temperature range, environmental exposure, and space limitations ensures consistent performance and longer operational life. Lithium cells excel in cold environments, while proper enclosures and insulation help protect against vibration, moisture, and heat.
- Cell configuration impacts performance and size: Series configurations increase voltage, while parallel configurations boost amp-hour capacity. Balancing these factors helps designers optimize power output without compromising enclosure space or stability.
- Conservative voltage windows extend battery life: Operating within a limited charge/discharge voltage range reduces stress on cells, prevents overcharging, and minimizes degradation. Staying within a conservative window (for example, 3.5V–4.0V instead of 3.5V–4.2V) enhances both safety and longevity.
- Depth of discharge (DoD) management improves cycle count: Limiting discharge depth to more conservative levels can add thousands of cycles to a battery’s lifespan. A shallower DoD, such as 20%, can extend cycle life by up to 30% compared to deeper discharges.
- Thermal management and BMS integration are essential: Effective heat dissipation, proper airflow, and the inclusion of advanced BMS features, like temperature monitoring, SoC/SoH tracking, and active cell balancing, help prevent thermal runaway, maintain consistent performance, and safeguard long-term reliability.
