A lithium battery in a portable medical device is simultaneously your enabler and your single biggest electrical-safety hazard. Under the MDR, battery selection, cell chemistry, battery management system design, charging architecture, thermal protection, end-of-life handling, and transport must all be evidenced in the technical file. EN 60601-1:2006+A1+A12+A2+A13:2024 sets the frame; your risk file has to carry the rest.

By Tibor Zechmeister and Felix Lenhard.

TL;DR

  • MDR Annex I §14 and §17 require that energy sources in a device do not compromise safety — batteries are explicitly in scope.
  • Portable medical devices are predominantly lithium-ion or lithium-polymer; both carry thermal runaway risk that must be controlled by design, not by luck.
  • EN 60601-1:2006+A1+A12+A2+A13:2024 includes specific clauses for batteries, charging, and internally powered equipment.
  • IEC 62133 (cell-level battery safety) is commonly cited by cell manufacturers.
  • Transport of lithium cells and batteries is governed by UN 38.3 and related rules.
  • Your instructions for use must carry clear battery handling, charging, storage, end-of-life, and transport statements under Annex I Chapter III §23.

Why this matters

A team building a portable infusion pump ran hot in production. Literally. Their chosen 18650 cell had excellent energy density and was sourced from a reputable supplier, but the battery pack integrator had changed the nickel strip thickness without telling them. The pack passed initial qualification. Six months into production, two units in the field showed abnormal temperature readings. The root cause was a cell that entered thermal runaway after an uncommon charging cycle, triggered by increased resistance at the tab weld.

Nobody was hurt. The company issued a field safety corrective action, recalled the field units, re-qualified the supplier, and redesigned the battery compartment with additional thermal isolation. It cost six months, a CAPA that turned into a 40-page document, and an unannounced audit the following year that dug into supplier controls for every critical component.

Batteries are not a "select a part, move on" decision. They are an ongoing system commitment.

What MDR actually says

Annex I §14.2 requires that devices be designed and manufactured so that risks associated with "energy sources" and "environmental conditions" are eliminated or reduced as far as possible. Battery chemistry, thermal behaviour, and failure modes sit squarely inside "energy sources."

Annex I §17.1 requires devices incorporating electronic programmable systems — including battery management systems — to be designed to ensure repeatability, reliability, and performance in line with intended use. If your battery management runs in firmware, that firmware is part of your EN 62304 software scope.

Annex I Chapter III §23 (information supplied with the device) obliges the manufacturer to include operating instructions, warnings, and precautions. For a battery-powered device, this includes charging, storage, end-of-life disposal, and handling under expected and foreseeable misuse conditions.

The harmonised standard reference for medical electrical equipment is EN 60601-1:2006+A1+A12+A2+A13:2024. Relevant clauses for batteries cover:

  • Internally powered equipment definitions and requirements
  • Battery type, marking, and replacement provisions
  • Overcharge and overdischarge protection
  • Short-circuit protection
  • Temperature limits under normal and single fault conditions
  • Mechanical integrity of battery enclosures and connectors
  • Leakage of battery electrolyte

Cell-level safety testing is commonly demonstrated via IEC 62133 (secondary cells and batteries containing alkaline or other non-acid electrolytes, for use in portable applications). — cell vendors will typically supply the test report; you inherit this evidence in your technical file as a supplier-provided input.

Transport of lithium cells and batteries is separately regulated by the UN Model Regulations on the Transport of Dangerous Goods, tested per UN Manual of Tests and Criteria, Section 38.3. ADR (road), IATA DGR (air), and IMDG (sea) all reference these tests.

A worked example

A team is building a Class IIa portable patient monitor with a 7.2 V, 3200 mAh lithium-ion battery pack (two 18650 cells in series).

Step 1 — Cell selection. The team evaluates three options:

  • Generic consumer cell, no UN 38.3 report on file, aggressive pricing.
  • Branded cell from a tier-1 manufacturer, UN 38.3 + IEC 62133-2 reports, mid-price.
  • Automotive-grade cell with full abuse test data, higher price, larger form factor.

The middle option is selected. The supplier provides the UN 38.3 test report and the IEC 62133-2 test report on letterhead. These documents join the technical file as supplier evidence.

Step 2 — Battery pack integrator qualification. The cells go to a pack integrator who adds the BMS board, protection circuit, thermistor, and enclosure. Under EN ISO 13485, the integrator is a critical supplier. The team performs a supplier audit, signs a quality agreement that includes change notification obligations (any PCB revision, any nickel strip change, any cell source change triggers a mandatory notification before shipment), and specifies the pack acceptance criteria.

Step 3 — BMS functional requirements. The battery management system must, at minimum:

  • Prevent overcharge (typical threshold: 4.25 V per cell, hard cutoff)
  • Prevent overdischarge (typical threshold: 2.5 V per cell)
  • Prevent overcurrent and short circuit
  • Monitor cell temperature and cut off charging above a defined limit (typically 45 °C) and below a defined limit (typically 0 °C)
  • Balance cells during charging
  • Report state of charge to the host device
  • Fail safe — any detected anomaly triggers a non-recoverable shutdown that requires a factory reset

If any of these functions is implemented in firmware, that firmware is subject to EN 62304. The team documents the BMS firmware as a software item within the device's software architecture.

Step 4 — Thermal architecture. The risk analysis identifies thermal runaway as a hazard with severe consequences. Risk controls include:

  • Cell spacing and mechanical isolation per vendor recommendation
  • Flame-retardant enclosure material
  • Thermal fuse in series with the pack, rated below cell autoignition
  • Active temperature monitoring with firmware shutdown
  • Vent path designed to direct any released gases away from the patient-facing surface of the device

Each control is traced from the 14971 hazard to the design requirement to the verification evidence.

Step 5 — Charging architecture. The device charges via a medical-grade external adapter (see the separate post on power supply safety). The charger provides regulated DC; the BMS manages the actual charging profile. The technical file evidences that only the specified charger is qualified, and the IFU warns against using any other.

Step 6 — End of life and replacement. The pack is not user-replaceable. The IFU and service manual specify authorised service for battery replacement, including ESD and thermal handling procedures. WEEE marking appears on the device. Disposal is handled via the WEEE and Battery Directive channels in each member state.

Step 7 — Transport. Finished devices ship with the battery installed. The logistics team ensures compliance with UN 38.3 and the applicable transport mode rules (IATA DGR for air, ADR for road). The team carries the UN 38.3 test report for the pack in the shipping dossier.

The Subtract to Ship playbook

Pick a chemistry and stick with it. Lithium-ion, lithium-polymer, lithium iron phosphate (LFP), and classic NiMH have very different trade-offs. LFP has lower energy density but materially better thermal runaway characteristics — for a clinical device where size permits, LFP can simplify your safety argument dramatically. Make this choice early.

Buy cells from vendors who can ship you the IEC 62133 and UN 38.3 test reports on day one. If a cell vendor cannot produce these within a week of request, they are not a medical device supplier. Move on.

Treat the pack integrator as a critical supplier from day one. Quality agreement. Change notification clause. Incoming inspection. First-article inspection. Sample retention. These are standard ISO 13485 supplier controls; apply them with full rigour to the battery pack. The quietest change control failure is a weld spec that drifts.

Specify the BMS as if it were a safety system. Because it is. Write a BMS requirements document. Review it like a safety-critical requirements doc. Verify every protection with fault injection during bench testing — force an overvoltage, force a short, force a thermistor open, force a thermistor short, force a communication loss with the host.

Design the enclosure to fail safely. Assume one cell will fail into thermal runaway. Design the compartment so that the failure does not propagate to adjacent cells, does not ignite the enclosure, does not release hot gases toward the patient surface, and gives the user a clear warning before the event becomes catastrophic. Fire-resistant materials, vent paths, and thermal isolation between cells are cheap compared to a field safety corrective action.

Write clear IFU statements. Under Annex I Ch III §23, the IFU must tell the user: approved charger only, operating temperature range, storage conditions, what to do if the device becomes hot, what to do if it has been dropped, and how to return the device for battery service or disposal. Plain language. Numbered steps. One page at most for battery-related instructions.

Plan the transport dossier. Sales fulfilment will hit transport rules the moment you ship your first unit. Have the UN 38.3 test report ready. Know which transport categories apply to your pack (watt-hour rating, number of cells). Include battery handling in your ship-kit documentation.

Think about end-of-life before launch. WEEE compliance and battery collection are member-state-level obligations. Register where required. Include the collection scheme reference in the IFU. Do not let this become a post-launch scramble.

Reality Check

  1. What cell chemistry did you choose and why? Can you articulate the trade-off in one sentence that references your clinical context?
  2. Do you have the IEC 62133 and UN 38.3 test reports for your cells on file, on supplier letterhead, with matching lot traceability to your first production build?
  3. Is your pack integrator a qualified critical supplier under your ISO 13485 QMS, with a signed quality agreement and a change notification clause that has teeth?
  4. Does your BMS implement all of: overcharge, overdischarge, overcurrent, overtemperature (hot and cold), and cell imbalance protection? Have you verified each with fault injection?
  5. What happens mechanically and thermally if one cell enters runaway? Have you tested this, modelled it, or at least drawn the failure path?
  6. If the BMS firmware is in your EN 62304 scope, at what software safety class is it? Do the architecture, verification, and configuration management records exist?
  7. Does your IFU contain clear, specific battery handling, charging, storage, and disposal statements, traceable to Annex I Chapter III §23?
  8. Is your finished-device transport dossier ready: UN 38.3 report, watt-hour labelling, category declaration, correct packaging for the shipping mode?
  9. Do you know the WEEE and battery collection scheme obligations in every member state where you plan to sell?
  10. When was the last time you reviewed a cell or pack change notification from your supplier? If never, either your suppliers are unusually stable or your change control has a silent gap.

Frequently Asked Questions

Is IEC 62133 required for medical device batteries under the MDR? Not directly. The MDR requires safe energy sources; IEC 62133 is the commonly accepted cell-level safety test that supports that argument. Treat it as the expected evidence level for lithium cells regardless of harmonisation status.

Do we need our own UN 38.3 test if we use certified cells? The UN 38.3 test applies to the cell and the battery assembly. A certified cell passes cell-level tests. A custom battery pack assembly generally needs its own battery-assembly tests, unless it falls under a small-assembly exemption. Check with your pack integrator and your transport compliance advisor.

Can we use a battery that is user-replaceable? You can. It adds risk — wrong battery installation, counterfeit replacements, ESD events during replacement — and the risk analysis must address each. Many startups choose fixed, service-replaceable batteries specifically to control this surface area. If you allow user replacement, the IFU instructions and the mechanical keying both have to be robust.

What about shipping units to customers in the EU by air? Air freight of lithium cells is tightly regulated under IATA DGR. Watt-hour rating drives the category. Packaging must be tested. Labels must be correct. Partner with a freight forwarder that handles lithium cells routinely — this is not the place to save money.

How should we handle battery end-of-life? Register with the national WEEE and battery collection schemes in each member state of sale, provide clear disposal instructions in the IFU, and include a return path for customers. Do not tell users to put medical device batteries in household waste.

Does our BMS firmware need EN 62304 documentation? If the BMS firmware contributes to safety functions — and for a lithium-ion pack, it almost certainly does — yes. Classify it per EN 62304 software safety class (A, B, or C depending on hazard), and produce the lifecycle documentation appropriate to the class.

Sources

  1. Regulation (EU) 2017/745 on medical devices, consolidated text. Annex I §14, §17, Chapter III §23.
  2. EN 60601-1:2006+A1+A12+A2+A13:2024 — Medical electrical equipment — Part 1: General requirements for basic safety and essential performance.
  3. EN ISO 14971:2019+A11:2021 — Application of risk management to medical devices.
  4. IEC 62133 series — Secondary cells and batteries containing alkaline or other non-acid electrolytes — Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications.
  5. UN Manual of Tests and Criteria, Section 38.3 — Lithium metal and lithium ion batteries.