How to Choose a Custom Lithium Battery Pack for Medical Devices?

Choosing the right battery pack for a medical device involves much more than matching voltage and capacity. Engineers also need to consider runtime, discharge current, size, weight, charging method, safety protection, connector design, operating environment, and certification requirements.

For portable medical equipment, monitoring systems, wearable devices, diagnostic instruments, and other rechargeable applications, the battery should ideally be evaluated together with the PCB and mechanical structure from an early development stage. This helps avoid problems such as insufficient runtime, excessive thickness, unstable peak-current performance, or costly redesigns later.

Below are the key questions engineers should consider when selecting a custom lithium battery pack for medical devices.

What Voltage Should a Medical Device Battery Use?

The required battery voltage depends mainly on the electronics architecture and power requirements of the device.

Common lithium battery configurations include:

• 1S: approximately 3.7V
• 2S: approximately 7.4V
• 3S: approximately 11.1V
• 4S: approximately 14.8V
• Higher-series configurations for larger portable equipment

Some compact medical devices can operate from a single lithium cell, while pumps, portable diagnostic equipment, mobile medical carts, or motor-driven systems may require higher-voltage packs.

GLOFLUX supports customized rechargeable battery configurations from approximately 3.7V to 72V, typically from 1S to 20S, depending on battery chemistry, capacity, discharge requirements, and application.

The best voltage should be selected together with the device's DC/DC conversion architecture rather than simply choosing the highest possible battery voltage.

How Much Battery Capacity Does a Medical Device Need?

Battery capacity should be calculated according to device power consumption and required operating time.

A basic calculation is:

Battery Energy (Wh) = Battery Voltage × Capacity (Ah)

For example, an 11.1V 2Ah battery provides approximately:

11.1V × 2Ah = 22.2Wh

However, real operating time can be lower because of:

• DC/DC conversion losses
• BMS power consumption
• Battery aging
• Low-temperature performance
• High-current loads
• Safety reserve requirements

For this reason, engineers should provide both the average operating current and expected runtime when requesting a custom battery.

Capacity should also be balanced against physical size and weight. A higher-capacity battery usually requires more cell volume, so maximizing capacity is not always the best solution for a compact medical device.

Why Are Continuous Current and Pulse Current Important?

Continuous discharge current is the current the battery must provide during normal operation over an extended period.

Pulse current is a short-duration peak load.

Medical and connected devices may experience current pulses during:

• Wireless data transmission
• Pump activation
• Motor startup
• Display brightness changes
• Alarm activation
• Sensor operation

A device may consume only 200mA during normal operation but briefly require 800mA or more.

Therefore, a battery manufacturer should ideally receive the following information:

• Typical operating current
• Maximum continuous current
• Peak current
• Pulse duration
• Time between pulses

This information allows the battery cell and BMS to be selected for stable voltage performance and safe operation.

LiPo or Cylindrical Li-ion: Which Is Better for Medical Devices?

Both lithium polymer and cylindrical lithium-ion cells can be suitable, but they serve different design priorities.

LiPo batteries are often preferred for handheld, wearable, or thin medical devices because the cell dimensions can be adapted more closely to the available space.

18650 or 21700 battery packs are generally more suitable for larger equipment requiring higher capacity, longer runtime, or stronger discharge performance.

LiFePO4 can also be considered where cycle life, thermal stability, or larger system capacity is a priority.

Can the Battery Be Designed Around the PCB?

Yes. In compact medical devices, the battery, PCB, enclosure, and connectors should ideally be designed together.

For example, if the PCB is circular or near-circular, engineers may evaluate a thin round battery or another geometry that reduces unused internal space.

In other designs, reducing battery thickness may be more important than achieving maximum capacity because a thinner battery can reduce the total thickness of the finished device.

During a custom project, GLOFLUX can evaluate:

• Cell dimensions
• PCB placement
• BMS location
• Wire direction
• Connector position
• NTC placement
• Enclosure integration
• Available mechanical space

Early coordination between the electronics and battery design teams can significantly reduce later mechanical changes.

What BMS Functions Are Important for Medical Battery Packs?

A battery management or protection system may include:

• Overcharge protection
• Over-discharge protection
• Over-current protection
• Short-circuit protection
• Temperature monitoring
• Cell balancing for multi-series packs

Depending on the device, additional functions may include NTC temperature sensing or communication interfaces.

The protection design should match the battery voltage, charging system, maximum current, and operating conditions rather than using a generic BMS.

What Certifications Should Be Considered?

Certification requirements depend on the battery, target market, transportation method, and final medical device.

Common battery-related requirements may include:

• UN38.3 for lithium battery transportation
• IEC 62133 where applicable
• CE-related requirements
• RoHS
• Other project-specific safety standards

It is important to note that battery certification does not replace certification of the complete medical device.

For example, UN38.3 mainly addresses lithium battery transportation safety. The final product manufacturer should determine the complete regulatory pathway for the finished medical device.

What Information Should Be Sent to a Battery Manufacturer?

For a faster engineering evaluation, provide as much of the following information as possible:

• Device application
• Required voltage
• Target capacity
• Maximum battery dimensions
• Continuous current
• Peak current and pulse duration
• Charging method
• Connector type
• Wire length
• BMS requirements
• Operating temperature
• Required certifications
• Prototype quantity
• Estimated annual volume

A drawing, 3D model, existing battery sample, or preliminary installation envelope can further improve the evaluation.

How Does GLOFLUX Support Custom Medical Device Battery Projects?

GLOFLUX supports custom rechargeable battery development using Li-ion, LiPo, 18650, 21700, and LiFePO4 technologies.

Depending on the project, customization can include:

• 3.7V–72V battery configurations
• Approximately 1S–20S designs
• Custom capacity
• BMS / PCM
• Connectors and wire harnesses
• NTC and communication requirements
• Battery enclosure integration
• Prototype development
• Testing and production support

For medical device developers, the most effective approach is to evaluate the battery together with the electrical and mechanical architecture rather than selecting it at the end of the design process.

If you are developing a portable medical device, diagnostic instrument, wearable monitor, or other rechargeable equipment, providing the application, voltage, capacity, available space, current profile, and expected quantity is usually enough to begin a preliminary battery engineering evaluation.