Batteries and Medical Devices

1 Start with the medical function

Before choosing a chemistry or capacity, ask what happens when power becomes unavailable or unreliable.

An infusion pump might stop delivering medication. A monitor might stop detecting a clinically important change. An analyser might interrupt an assay, lose a result or attach an incorrect timestamp. A backup cell can therefore matter even when it never powers the main medical function.

Define which functions must continue, for how long, and which may stop safely. Include the energy needed to detect a problem, warn the user, preserve records and reach the required state.

Stopping immediately is not always the safest response. Depending on the clinical use, the device might need to complete a controlled action, transfer to another supply or maintain an alarm. These decisions belong in the device risk analysis.

ISO 14971 provides the medical device risk-management framework. The examples and checklists in this module are engineering prompts to apply within that framework.

2 Understand the battery terminology

A fully charged aged battery may deliver much less runtime than a fully charged new battery. Also distinguish calendar ageing, which occurs over time, from degradation associated with charge and discharge cycles.

“Lithium” alone is not a sufficient specification. Primary lithium and rechargeable lithium-ion batteries need different treatment. A rechargeable coin cell must not be substituted for a primary coin cell simply because it fits the holder.

3 Choose a battery against the use case

These are selection prompts, not a ranking. Compare actual qualified products and supplier data under the intended operating conditions.

Build a power budget covering standby, start-up, measurement, motors, heaters, radio transmission, alarms and shutdown. Both average demand and peak current matter. A battery may contain enough energy but still fail to support a short current pulse without excessive voltage drop.

4 Estimate runtime and then verify it

For an initial estimate:

Runtime in hours ≈ nominal energy in Wh × usable fraction × conversion efficiency ÷ average load in W

Illustrative assumptions:

• Nominal voltage: 3.7 V.
• Rated capacity: 2.0 Ah.
• Nominal energy: 7.4 Wh.
• Usable fraction after allowing for the chosen operating limits: 0.80.
• Conversion efficiency: 0.90.
• Average load at the device supply rails: 1.0 W.

The estimated runtime is 7.4 × 0.80 × 0.90 ÷ 1.0 = 5.33 hours.

This is a design estimate, not evidence for a labelled runtime claim. The assumed usable fraction must be justified. Assess ageing, temperature, production variation, cut-off voltage and the real operating profile; avoid counting the same loss twice.

A credible runtime requirement describes the operating mode, environmental conditions, battery condition and endpoint. For example, define whether “runtime” ends at the first low-battery warning or when the required medical function can no longer be maintained.

Voltage alone may give an inadequate estimate of remaining runtime. Battery-gauge behaviour depends on the chemistry, model, load and temperature. Texas Instruments explains these interactions and the risk of unexpected shutdown.

5 Analyse hazards across the whole system

Do not restrict the analysis to fire. Loss of the medical function may be the dominant risk.

For connected equipment, consider whether repeated communications, unauthorised commands or software faults could exhaust the battery or alter power-management settings. Where relevant, link those scenarios to both cybersecurity and safety risk management.

6 Select standards by chemistry and application

There is no single battery standard that covers every medical device.

Establish the equipment’s scope and relevant particular requirements. Industrial, stationary and implantable applications may need other standards.

The editions above were checked against public publisher information on 1 October 2026. A publisher’s latest edition is not automatically the edition recognised, harmonised or otherwise accepted in every market. Record the chosen editions, amendments, national differences and transition arrangements in the project standards plan. Full normative texts are needed for a clause-by-clause assessment.

7 Integrate charging and protection

Specify the complete charging path: external supply, cable, connector, charging circuit, battery protection, temperature sensing and control software.

Useful design questions include:

• Can the device operate while charging, and has that combination been assessed?
• What prevents charging at an unsuitable temperature or with a failed temperature sensor?
• What happens after deep discharge, prolonged storage or repeated interrupted charging?
• Can a wrong power source or replacement battery be connected?
• Which protective functions remain effective when application software stops responding?
• Could a common failure defeat both monitoring and protection?

Use the selected cell manufacturer’s limits and the device risk analysis to establish protection. Avoid treating a generic USB connector, a charger IC or a supplier’s “protected battery” description as proof that the complete charging system is suitable.

Where a protective function is safety-related, define its independence and behaviour under the relevant faults. A software-controlled action may need additional protection depending on the hazard and applicable requirements.

8 Define power failure and recovery behaviour

Battery behaviour is also a software and usability issue.

Define the response to low energy, critical energy, sudden battery disconnection, mains failure, restoration of power and invalid battery-status information.

For each event, specify:

• The medical function that continues, stops or changes.
• The warning and action available to the user.
• The information that must be preserved.
• The status assigned to an interrupted measurement or treatment.
• The checks required before restarting.
• Whether automatic resumption is permitted.

Protect records against incomplete writes. A partially completed assay should not appear as a valid completed result. A therapy device should not repeat a delivery simply because it restarts.

Verify transitions as well as steady operation. Repeated changes between external power and battery, brief voltage dips and a nearly exhausted battery can expose problems that a simple runtime test misses.

9 Plan verification around claims and risks

Use supplier evidence where it applies, then address the integration and device behaviour that the supplier has not tested.

This is a planning checklist, not a mandatory universal test sequence. Select conditions, samples and acceptance criteria from the requirements, applicable standards and risks. Justify representativeness of samples and ageing methods.

Potentially destructive battery-abuse testing requires appropriate facilities and controls. Existing valid supplier or laboratory reports may support the assessment when they cover the actual configuration and conditions.

10 Manage transport separately from operational safety

For lithium batteries, distinguish batteries shipped alone, packed with equipment and contained in equipment. Chemistry, configuration, energy or lithium content, condition and transport mode affect the shipment requirements.

UN 38.3 evidence addresses battery design-type testing. It does not replace finished-device safety assessment or establish that the packaged analyser, pump or monitor will survive its distribution route. PHMSA provides information on lithium battery test summaries.

Ask the supplier for the applicable test summary and supporting evidence, matched to the supplied cell or battery model. Check whether a custom pack or design change introduces additional assessment or testing.

For air freight, use the current rules and applicable packing instruction. State-of-charge restrictions and packaging provisions depend on the shipping configuration; do not apply a single percentage to every shipment. IATA’s battery transport resources explain the relevant classification and shipping framework.

Include prototype shipments, spare batteries and returns in the logistics plan. Damaged or defective batteries need separate assessment; the normal delivery process may be unsuitable.

11 Control suppliers and the service lifecycle

A supplier’s certificate is useful only when its scope matches what you buy and how you use it.

Obtain the exact cell and pack identities, specifications, test evidence, charging limits, storage conditions, traceability arrangements and change-notification commitments. Clarify whether reports cover a cell, the assembled pack or both.

Control changes to the cell manufacturer, chemistry, protection circuit, connections, enclosure, firmware and charger. Similar dimensions and nominal ratings do not establish equivalence.

Define replacement criteria using suitable evidence, such as remaining capacity, internal resistance, age, cycle history or device diagnostics. A calendar interval or “80% capacity” threshold must be justified for the application rather than copied as a universal rule.

Provide instructions for storage, charging, approved replacements, warning responses and disposal. Plan how a technician restores sealing, verifies operation and deals with a depleted backup cell.

For EU products, also assess the Batteries Regulation, Regulation (EU) 2023/1542. Applicability, phased dates and removability or replaceability provisions require a product-specific review. Do not assume all medical devices are exempt.

Monitor field complaints and service data for unexpected shutdowns, swelling, charging faults, accelerated ageing and recurring replacement errors.

12 Worked examples

Rechargeable infusion pump

A fictional pump is intended to operate during patient transfer. The development team must translate that use into requirements for operating duration, delivery profile, alarms, changeover and reserve.

The assessment includes the rechargeable battery and charger, the applicable equipment standards, and the clinical consequences of interruption. Verification uses justified battery conditions and demanding delivery loads, and checks that the low-battery warning leaves enough time for the defined user action.

An abrupt battery-protection cut-off may prevent battery damage while still creating an unacceptable interruption of therapy. Both behaviours need to be considered.

Mains powered IVD analyser with a backup coin cell

A fictional analyser contains a primary lithium coin cell that maintains its clock. It cannot perform an assay from that cell.

IEC 60086-4 is a relevant starting point for the primary lithium battery; IEC 62133-2 is not the appropriate selection merely because the cell contains lithium. Assess the analyser under its applicable equipment safety framework.

The development questions include inadvertent charging, cell retention, service replacement, depletion detection and timestamp validity. If a reset clock affects result records or security checks, the analyser needs defined behaviour for detecting and correcting the condition.

A small internal cell is still part of the device configuration and must be considered in the applicable transport assessment.

13 Practical exercise

Choose a real or fictional battery-containing device. Write a one-page battery assessment answering these questions:

1. What does each battery power or preserve?
2. What happens if it depletes, disconnects or provides unstable power?
3. Which chemistry, cell and pack configuration are proposed?
4. Which battery, equipment and transport requirements need assessment?
5. What are the runtime, storage, charging and replacement claims?
6. What evidence is available from the supplier, and what device evidence is still needed?
7. What would cause you to reject a proposed battery substitution?

Discussion prompts

A supplier offers an IEC 62133-2 report for a replacement primary lithium coin cell. What should you do?
Resolve the mismatch in chemistry or documentation and obtain evidence appropriate to the actual battery. Do not accept the report solely because its title mentions lithium.

A new battery passes the runtime test at room temperature. Is the runtime claim established?
Only for the tested conditions. The intended claim also needs support for the relevant operating profile, environment, variability and battery life.

The pack has passed UN 38.3. Can the complete device be released?
That evidence supports the transport assessment. Release still depends on applicable device requirements, integration evidence and shipment arrangements.

The battery displays 100% charge. Does that mean it is healthy?
No. The battery may be fully charged relative to its reduced available capacity.