19.8 kg Lighter, No Scheduled Overhauls: Heli Austria and Heli Werk Launch EASA-Approved Lithium Battery Upgrade for All EC135/H135 Models — an "Invisible Upgrade" for HEMS Fleets

Published: October 10, 2026  |  Category: Industry

This site has previously covered SKYTRAC's 40 years and aviation medicine's data-driven future, and has followed EC135/H135 fleet safety events closely (including the October 4 H135 crash off Catalina Island, California). This time, the news is good. Per a Vertical Magazine report of October 7, 2026, Austrian helicopter operator Heli Austria and German aviation products manufacturer Heli Werk have introduced an EASA-approved lithium battery upgrade applicable to all Airbus EC135/H135 models — including Helionix-equipped aircraft. The EC135/H135 is one of the world's most widely operated light twin helicopters in HEMS (helicopter emergency medical services). This "invisible" battery modification bears directly on the payload, readiness and maintenance cost of every medical helicopter now flying.

1. The Solution Itself: TB30/TB40 Lithium-Ion Replacing NiCad, Up to 19.8 kg Lighter

According to the Vertical Magazine report and Heli Werk's official product page, the technical core of the upgrade is straightforward: replace the aircraft's conventional nickel-cadmium (NiCad) batteries with a TB30 or TB40 lithium-ion battery system. The two options weigh in as follows — TB30: 30 Ah capacity at 12.6 kg; TB40: 40 Ah at 16.7 kg. Depending on the aircraft's existing battery configuration, operators can achieve up to 19.8 kg of weight reduction and up to 15 Ah of additional capacity. What does 19.8 kg mean in practice? For a light twin with a maximum take-off weight around 2.9 tonnes, that is roughly the weight margin of an adult passenger — convertible into additional medical equipment, more fuel, or extra performance margin in hot-and-high conditions. Equally important is the change in maintenance regime: the solution operates on-condition, eliminating scheduled battery overhauls. NiCad main batteries conventionally require periodic removal for capacity checks and refurbishment; lithium systems are monitored in service instead. That directly cuts battery-related maintenance man-hours, shop logistics and — most valuable of all — aircraft downtime.

2. The Certification Path: STC 10090942 + Part 21G Production Approval — a Textbook "Design–Production" Split

The compliance architecture behind the modification deserves industry attention. The project was developed and certified by Heli Austria, which holds the EASA Supplemental Type Certificate STC 10090942 (under its Part 21J design organisation approval); Heli Werk manufactures the complete upgrade kits under EASA Part 21G production approval DE.21G.0251, with production parts released on EASA Form 1. Each kit includes the selected battery system, all components required for installation, and the applicable STC documentation. The two managing directors' remarks in the report capture the logic of the partnership. Joachim Kies of Heli Werk: "EC135 operators can now choose a complete upgrade solution that combines lower weight, higher capacity and reduced scheduled battery maintenance. Our focus was to turn the approved design into a production-ready kit supplied with the required installation components and documentation." Roy Knaus of Heli Austria: "Working with Heli Werk went smoothly from start to finish. The close coordination between design and production helped us move the project through certification and deliver a solution that is ready for operators." For operators, the complete chain — design approval plus production approval plus Form 1 release — means the modification can be installed at any appropriately rated maintenance organisation rather than being locked to a single supplier. That is precisely what determines whether a retrofit scales.

3. Why the EC135/H135: The Multiplier Effect of HEMS's Workhorse Type

Choosing the EC135/H135 as the modification target is no accident. Since entering service in the late 1990s, this family has long held a dominant position in European — and global — HEMS fleets: Germany's ADAC air rescue, multiple UK air ambulance networks, Ambulance services in Australia including New South Wales, and many US operators including Reach Air Medical fly EC135s or the upgraded H135. A large installed base means any approved retrofit is amplified across the entire HEMS network. Placed back into the concrete reality of medical operations, the battery upgrade's value shows on at least three levels. First, weight saved is payload and range. The cabin of a medical helicopter is priced by the kilogram: stretcher, ventilator, monitor, ECMO transport module, drug boxes — plus physician, flight nurse and pilot. Every kilogram freed from the battery comes straight back to mission payload or fuel, a tangible gain for mountain, island and hot-climate medical rescue. Second, downtime avoided is readiness. HEMS operates on an all-weather standby, minutes-to-launch promise; every scheduled maintenance window erodes standby time. Eliminating periodic battery overhauls structurally lifts annual fleet availability — for operators under government medical-rescue contracts, that is contract performance itself. Third, electrical power is medical-equipment assurance. Onboard medical devices depend on the quality and capacity of the electrical supply; the additional 15 Ah thickens the buffer for parallel device operation, ground standby power and emergency electrical supply. The Catalina Island H135 crash reported by this site in early October is a fresh reminder that the night, overwater, patient-on-board combination demands higher reliability from every subsystem — and the battery, small as it is, is the common source of engine start, avionics and emergency power.

4. Industry Context for Lithium Onboard: From "Can It Be Installed?" to "How Is It Managed?"

Lithium-ion main batteries have been a gradual trend in rotorcraft for years, but the bar has always been high: thermal-runaway risk, charge management, cold-weather performance and full-life monitoring all require complete design-certification backing — the essential difference between an EASA STC and an unapproved DIY modification. On-condition operation in this solution presupposes that the battery system carries its own health monitoring, with operators surveilling condition per the manual rather than tearing down on a fixed calendar. It points to an industry direction: the future competitiveness of aviation batteries lies in management systems, not cells alone. Whoever masters charge-discharge curves, state-of-health (SoH) assessment and remaining-life prediction can make on-condition maintenance real. The SKYTRAC flight-data story covered earlier by this site and this battery retrofit point to the same trend: air medical fleet maintenance is shifting from calendar-based to data-driven, condition-based regimes. For HEMS operators, the sooner a fleet's own battery-health data accumulates, the stronger its hand in retrofit decisions, insurance pricing and residual-value management.

5. Three Reference Points for China's Air Medical Fleets

China's air medical rescue fleets are likewise built around light twins — EC135/H135 (including domestically assembled variants), AW109 and Bell types — so this European approval carries direct mirror-image significance. 1) Approved retrofits of the installed base improve fleet capability faster than new purchases. China's HEMS fleets are relatively young but growing quickly; beyond new acquisitions, operators should actively track the STC upgrade list available for their types (batteries, avionics, medical-equipment mounts) and use modifications to extend the performance life of the fleet. 2) The "design–production" division of labour in airworthiness modifications is worth learning. Europe's pairing of a Part 21J design approver with a Part 21G production organisation lets a retrofit industrialise quickly and become installable at multiple maintenance sites. If China's general aviation maintenance industry is to serve medical fleet upgrades, matching modification-design and production-approval capabilities need to be built faster. 3) Maintenance downtime belongs inside medical-rescue network capacity planning. A medical helicopter's annual availability directly determines the real coverage of a rescue network; when planning regional HEMS bases and reserve capacity, scheduled maintenance windows should be made explicit. The importance of upgrades like "no more scheduled battery overhauls" is exactly this: they hand time previously locked in the maintenance plan back to standby duty.

Per Heli Werk's product page, the specific kit selection (TB30 or TB40), achievable weight reduction and installation scope depend on each aircraft's existing configuration and must be evaluated airframe by airframe. This site will continue to follow the lithium transition of EC135/H135 fleets.

Disclaimer: The facts in this article are drawn from Vertical Magazine's report of October 7, 2026, "Heli Austria and Heli Werk introduce EASA-approved lithium battery upgrade for all H135 models," and from Heli Werk's official product page, accessed and verified on October 10, 2026. The TB30/TB40 battery specifications (30 Ah/12.6 kg; 40 Ah/16.7 kg), the up-to-19.8 kg weight reduction, up-to-15 Ah capacity increase, on-condition operation, EASA STC 10090942, Heli Werk production approval DE.21G.0251, EASA Form 1, kit contents, and the quotations from Joachim Kies and Roy Knaus are all content of those sources; applicable models are as defined by the STC documentation. The industry analysis and China reference points are general discussion and do not constitute medical, investment or business advice; specific modification matters are subject to the approval documents of the competent airworthiness authority. In a medical emergency, call your local emergency number immediately.