Applications often require custom battery packs when off-the-shelf solutions cannot satisfy performance, packaging, safety, or industry-specific requirements. In these situations, battery chemistry, power demands, charging requirements, safety features, enclosure design, material selection, and certification planning all influence the final battery pack design.
Addressing these factors early in development helps align the battery pack with application requirements and can reduce delays later in the design and testing process.
Define Power and Capacity Requirements First
The starting point for any custom battery pack design is understanding the application's power consumption and runtime requirements.
Three key questions typically need to be answered:
- How much energy must the battery pack store?
- How quickly will the application consume that energy?
- How long must the application operate before recharging?
Power consumption is measured in watts (W), while stored energy is measured in watt-hours (Wh). Together, these values determine the battery capacity needed for the application.
For example, if a device requires 50 watts of power and must operate for 4 hours, the required battery capacity can be calculated as:
50 watts × 4 hours = 200 watt-hours (Wh)
In this case, the battery pack must provide approximately 200Wh of capacity.
The same information can be used to estimate operating time when multiple devices are connected to a battery pack. If a battery pack has a capacity of 200Wh and the connected devices consume a combined 60W, operating time can be estimated as:
200Wh ÷ 60W = 3.33 hours
Establishing power and capacity requirements early helps determine:
- The number of battery cells required
- Suitable battery chemistry options
- Overall battery pack architecture
- Enclosure design considerations
Calculate Charging Requirements for the Battery Pack
The charger must be matched to the battery pack's electrical requirements.
While both custom and off-the-shelf chargers are available, a charger designed specifically for the battery pack helps ensure the correct amount of energy is delivered. Proper charging can help avoid overcharging, undercharging, battery damage, and capacity loss.
Battery charging requirements are largely based on voltage and the configuration of the cells within the pack. Each battery chemistry has a nominal cell voltage.
Examples include:
- Lithium-ion: 3.6V nominal
- NiCad: 1.2V nominal
- NiMH: 1.4V nominal
Battery packs may deliver voltages higher than a cell's nominal voltage. For example, a battery with a nominal voltage of 3.6V may provide 4.2V for the application.
When determining charger requirements, the voltage provided by the charger must correspond to the number of cells in the pack.
For example, a battery pack containing four lithium-ion cells with a nominal voltage of 3.6V per cell would require:
4 cells × 3.6V = 14.4V
In this example, the battery pack would require a charger capable of providing 14.4V.
Incorporate Appropriate Safety Features
Safety requirements vary depending on the battery chemistry used in the design.
Lithium-ion batteries contain chemistries that may present risks such as thermal runaway, fire, or explosion. As a result, many national and international regulations require a battery management system (BMS) for lithium-based battery packs.
Battery pack being manufactured with BMS and custom enclosure.
A battery management system can provide:
- Temperature monitoring
- Current regulation
- Voltage regulation
- Thermal management
Additional protective functions may be incorporated based on factors such as:
- Operating environment
- Charge and discharge rates
- Vibration exposure
- Venting requirements
- Application-specific conditions
Cell Balancing Considerations
Cell balancing is another important safety and performance feature. The purpose of cell balancing is to ensure that individual cells maintain similar states of charge throughout operation. Without balancing, some cells may become overcharged or over-discharged relative to others.
Cell balancing approaches include:
- Active balancing, which redistributes charge between cells
- Passive balancing, which dissipates excess charge, so all cells maintain the same state of charge (SoC)
Maintaining balanced cells supports battery pack performance and helps prevent uneven charging or discharge conditions.
Selecting Materials Based on Application Requirements
Material selection affects both battery performance and the ability of the pack to withstand operating conditions.
Battery construction materials include:
- Anodes
- Cathodes
- Electrolytes
- Separators
- Internal electrical connections
Material choices depend largely on battery chemistry.
Examples include:
- Lithium, graphite, or silicon anodes for lithium-based cells
- Zinc-powder gel used in alkaline batteries
- Foam separators
- Electrolytes ranging from potassium hydroxide to lithium hexafluorophosphate
- Nickel-strip internal connections
Material selection should account for the conditions the battery pack will experience during operation, including application stresses and loads.
Industry-specific requirements may also influence material choices. Applications in sectors such as military & defense and medical may require specific material considerations. In other cases, budget constraints may influence whether lower-cost materials can be used while still supporting battery pack performance and quality objectives.
Design the Battery Enclosure Around the Application
The battery enclosure is another critical element of a custom battery pack design. A battery enclosure may be integrated within a device or installed in a separate compartment.
Common enclosure approaches include:
- Metal casings
- Shrink-wrap designs
- Vacuum-formed plastic enclosures
The enclosure should be selected based on factors such as:
- Protection of the battery cells
- Protection of the end user
- Exposure to environmental hazards
- Overall appearance requirements
Balancing these considerations helps ensure the enclosure supports both functional and application-specific requirements.
Plan for Certification Requirements Early
Certification requirements vary based on battery chemistry, industry, and intended market. Lithium-based battery chemistries require certification, while other battery types may require certification depending on industry expectations or application requirements.
Battery pack with certification markings on the enclosure.
Some manufacturers also pursue certification to support product marketing efforts and demonstrate adherence to established quality and testing standards.
Determining certification requirements depends on the standards established by the certifying organization.
Examples include:
- UL
- IECEE
- IEC
Certification programs may require multiple battery packs for testing, along with associated testing costs.
Account for Testing Time and Certification Schedules
Battery testing and certification activities can influence project timelines and product launch schedules.
Testing costs vary based on the certifying organization and the number of battery packs submitted for evaluation. Testing schedules may range from 4 weeks to 12 weeks, depending on the organization conducting the testing.
Because certification activities can affect overall lead times to market, testing schedules should be incorporated into the battery pack development timeline as early as possible.
Summary
A successful custom battery pack design begins with clearly defined power, capacity, charging, and safety requirements. Once those parameters are established, material selection, enclosure design, and certification planning can be aligned with the application's performance and regulatory needs.
Evaluating these considerations early in the design process helps support a battery pack solution that is properly matched to its intended use.
Key Takeaways
- Power requirements drive design: Calculating watt-hours (Wh) and device runtime is the first step in determining how many cells are needed and which battery chemistry is best suited for the application.
- Charging must match the pack: Custom battery packs should be paired with chargers designed specifically for their voltage and cell count to avoid overcharging, undercharging, or reduced capacity.
- Safety features are essential: Battery Management Systems (BMS) provide protection against overcharge, over-discharge, overheating, and imbalance between cells, helping prevent failures and hazards like thermal runaway.
- Enclosure and materials matter: Proper selection of electrode materials, separators, and pack housing (metal, shrink-wrap, or molded plastic) ensures performance, durability, and compliance with application-specific demands.
- Certifications impact marketability: Meeting regulatory standards such as UL or IEC not only satisfies industry safety requirements but also supports customer confidence and speeds adoption in regulated industries.
