Polymer Lithium Battery Solution for Insulin Pumps

In devices such as insulin pumps, the battery is never just a “power supply.”
It is a system-level component that directly affects dosing accuracy, safety, and long-term stability.

From real project experience, many issues that seem to be “control or software problems” can often be traced back to the power source, such as:
instant voltage drop, uncontrolled temperature rise, battery swelling in later life cycles, or failure to activate after transport or long-term storage.

This is why the requirements for an insulin pump lithium battery are much higher than those for ordinary wearable products.

I. Electrical Parameter Design Around the Pump Motor

Insulin pumps usually use high-precision DC gear motors or miniature stepper motors.

Their common characteristics are:

1. Very low average operating current
2. Short but noticeable current peaks during motor start-up and dosing

If battery internal resistance is not well controlled, or if discharge capability is insufficient, voltage sag can occur during dosing.
This may affect dosing consistency, or in severe cases, trigger system protection and false alarms.

Based on this, battery parameters are not “the higher the better,” but should match the real load characteristics of the system.

Recommended Key Electrical Parameters

1. Nominal Voltage: 3.7V / 3.8V
This is a mature and stable lithium polymer platform. It is easy to match with high-efficiency DC-DC buck circuits and helps reduce overall power consumption.

2. Rated Capacity: 500mAh – 800mAh
Under real use conditions with Bluetooth always on and occasional backlight use, this supports about 3–7 days of operation while balancing size and user experience.

3. Charge Cut-off Voltage: 4.20V ±0.05V
Medical devices must strictly avoid overcharging. Hardware-level protection is recommended, with overcharge protection set below 4.3V.

4. Discharge Cut-off Voltage: 3.0V – 3.2V
A “data retention zone” below 3.0V is usually reserved to protect RTC, logs, and critical parameters.

5. Maximum Continuous Discharge Current: 1C (about 500mA)
The goal is not high C-rate, but stable voltage during motor start-up.

6. Transport / Storage Quiescent Current (Ship Mode): < 10μA
This is often overlooked. Low quiescent current ensures the product can still be activated after six months of storage.

II. Thermal Management for On-Body Wear

Lithium batteries are highly sensitive to temperature.
At the same time, insulin pumps are worn close to the body for long periods, with typical skin temperatures around 35°C.

More importantly, insulin itself is sensitive to heat.
If local temperature control fails, it affects not only battery life, but also medication safety.

Recommended Temperature Limits

1. Discharge Temperature: –10°C to +55°C
Covers cold and hot outdoor environments.

2. Charge Temperature: +10°C to +45°C
Low-temperature charging increases lithium plating risk, while high-temperature charging increases swelling and aging.

At the hardware level, it is recommended to place an NTC thermistor near the center of the cell, rather than relying only on case temperature.
In system logic, charging should stop immediately when battery temperature exceeds 48°C, with a clear temperature warning.

In mechanical and thermal design, the battery should be isolated from heat sources such as the motor and main SoC.
Nano aerogel or graphite heat spreaders can be added to prevent long-term local hot spots from affecting the cell and insulin reservoir.

III. Size, Structure, and Reliability Design

To achieve a more discreet wearing experience, the internal space of an insulin pump is usually very limited.
This makes a highly customized battery almost mandatory.

Common Custom Size Ranges

1. Thickness: 4.0 – 6.0 mm
2. Width: 20 – 30 mm
3. Length: 30 – 45 mm

Compared with standard batteries, custom-shaped cells significantly improve space utilization and allow more freedom in thickness and industrial design.

In most projects, pouch-type lithium polymer cells are preferred.
They are lighter, and in extreme failure conditions, they usually swell instead of rupturing, which is more suitable for wearable medical devices.

One key point is that at least 10% swelling allowance must be reserved in the thickness direction during mechanical design.
If battery swelling in later life presses directly on the PCB, it can easily cause false pressure or flow sensor readings. This is a very common failure mode in real projects.

In addition, since the battery is often the heaviest component inside the pump, PORON foam is recommended around the battery to reduce damage to solder joints and housing during drops.

IV. Regulatory and Certification Requirements

Any battery solution used in insulin pumps must consider the certification path early.
Otherwise, projects can easily be blocked at a late stage.

Common required standards include:

1. IEC 62133-2 (Lithium battery safety)
2. UN 38.3 (Air transportation)
3. UL 2054 (Battery pack safety)
4. ISO 13485 (Medical device quality management system)

From practical experience, a battery supplier’s familiarity with medical certification processes is often more important than the raw specifications alone.

MOTOMA: Custom Lithium Battery Solutions for Insulin Pumps

In insulin pump applications, there are very few truly “off-the-shelf” battery solutions.
This is exactly where MOTOMA lithium polymer batteries stand out.

MOTOMA provides not just individual cells, but complete system-oriented medical lithium battery solutions:

1. Support for 3.7V / 3.8V platforms with flexible capacity and size customization
2. Optimized internal resistance and discharge structure for motor peak loads
3. Ultra-thin and custom-shaped pouch cells for complex industrial designs
4. Integrated solutions including NTC, protection circuits, and connectors
5. Experience with long-term supply stability and consistency for medical projects

For wearable medical device design, this means greater design freedom without sacrificing safety or reliability, while reducing long-term failure and certification risks.

Competition in insulin pumps is no longer just about algorithms or appearance.
It reflects overall system engineering capability.

The battery, as the most basic yet often underestimated part, frequently determines whether a product can operate safely and reliably over the long term.
Through load-matched electrical design, strict thermal control, proper mechanical allowance, and reliable customization capability, a lithium polymer insulin pump lithium battery truly becomes the “safety foundation” of the system.