Portable consumer electronic devices have transformed our daily lives and while some may argue whether the proliferation of such devices has actually improved our lives it is difficult to refute the impact they have had on the way we all communicate and interact with each. It may be a cliché, but none of these portable devices would exist if it were not for the batteries that power them.
There are many users who will shake their heads in disagreement when told that battery technology is keeping pace with technological development because at first glance, it does not seem to do that. However, I am sure that even Gordon Moore himself appreciates the technical challenges associated with providing such a large amount of chemical energy in a small space, while ensuring it is safe, reliable, cost effective and reusable.
Today everyone expects portability in their professional lives as we all strive for greater flexibility and operability. One important area that has seen a proliferation of battery-powered portable devices is the healthcare sector.
There are many reasons for taking an existing medical device and equipping it with battery power, but the most common is the option to carry it around and use it when and where is needed. Whether this is so that the clinician can work more efficiently or so that patients do not need to move from their beds, battery-powered portable medical equipment provides greater flexibility and freedom.
Portable medical devices need high gravimetric and volumetric energy density and cobalt based cathode and lithium-ion (Li-ion) cell technology found in mobile phones, high end notebook computers or tablets, is typically used to meet this need. No other commercially available battery technology comes close to providing the wide range of performance attributes.
Reliable medical devices
There are many other medical devices that need batteries, but not for reasons of portability. These ‘transportable’ devices are usually pushed around on wheels and need a battery either when the device is being moved or when the mains electricity supply fails.
Patient lifts and acute ventilators are typical examples of transportable medical devices that need reliable batteries. For these applications, high voltage and discharge rate capability are the most important performance attributes. Here, medical device OEMs are moving away from the older nickel and lead based chemistries, due to their low energy density and high environmental impact.
The focus is now shifting to specialist Li-ion chemistries that have emerged for high drain applications. Li-ion cathode chemistry that utilises a mixture of nickel, cobalt and manganese offers an enviable combination of performance traits such as capacity, power delivery and safety, which makes it ideal for these demanding applications.
The rate of technological change seen in consumer electronic devices over the past decade has been staggering. Medical device OEMs are at the forefront of adopting many of these technologies into their devices. The rate of change is, however, a double-edged sword and whereas the product life cycle of a mobile phone may be twelve to eighteen months, the service life of medical equipment frequently exceeds ten years.
This need for technical aftercare requires a sustainable approach to both product design and purchasing to ensure that component obsolescence does not render a product unable to be serviced during its planned lifetime.
Although only part of the entire medical device, the impact of component obsolescence and in particular cell supply cannot be ignored. Until the start of this century, battery manufacturers made cells to defined international mechanical standards and device manufactures designed their devices around the cells.
The change occurred after the invention of Li-ion and Li-ion polymer cell technology and the trend of vertically integrating batteries into device manufacturing. This shift has led to the development of customised cells, which in turn has offered medical device manufacturers the option to produce the ideal device for their customers, in accordance with their specifications. Yet the relentless pursuit of smaller devices means that a cell produced in its millions last year may very well be obsolete and unobtainable next year.
For medical device OEMs this poses a real problem: how to use the latest battery technology and still be able to support devices in the long term for the next 10-15 years. The answer is to work in close collaboration with a battery developer that monitors both battery and device trends and can be truly unbiased when advising customers on cell selection.
Using cells across a broad range of markets that conform to established mechanical standards provides reassurance of long term availability. Furthermore, designing for redundancy allows fitting of alternative sizes if the worst were to happen and a certain type of battery became hard to find.
Electrochemistry is constantly evolving and medical OEMs must avoid a situation where a future cell technology cannot be used because either the device or the charger is unable to cope with the ‘upgrade’.
The adoption of smart battery technology (SBT) allows batteries to be made future-proof. This type of technology puts the battery in control, allowing it to broadcast its need for both charging voltage and current, which is then provided by a smart charger in the device. When the battery is full it simply orders the charger to stop drawing current.
As each battery is programmed with the characteristics of the cell technology it contains, any future battery technology is automatically catered for, even if it has a different charge-voltage profile or capacity. It is even possible to use completely different battery chemistries such as nickel metal hydride (Ni-MH) and Li-ion on the same device and charger platform.
Certification and regulation
Batteries used in medical devices require special certification. While medical devices are certified to EN60601-1 (currently in its third edition), IEC62133 is required for cells. A CB certificate from a nationally recognised testing laboratory (NRTL) must be made available as well.
In addition, if the battery uses Li-ion cell technology, then their transportation is regulated whether by air, sea or road. Such batteries must meet the requirements of the United Nations Manual of Tests and Criteria part III subsection 38.3.
Li-ion batteries of more than 100Wh must also be tested and must always be shipped as class nine dangerous goods. This mean that careful consideration should be made when specifying such a high-capacity battery, as it can have implications for the entire distribution chain.
In summary, Li-ion battery technology allows medical device OEMs to free devices from mains electricity supply and offer clinicians and patients the flexibility and freedom that they experience with consumer devices. If attention is given at the outset to the future developments in cell technology, then it is possible to design a battery platform that can be continually upgraded over the product life cycle of the device, even if it might not quite keep up with Moore’s law.
Neil Oliver is technical marketing manager at Accutronics