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Choosing the right battery for medical devices

Posted: 07 Apr 2015 ?? ?Print Version ?Bookmark and Share

Keywords:batteries? chargers? medical device? IEC62133? ISO13485?

In the movie "Hours" starring the late actor Paul Walker, one of the key themes revolves around the effectiveness of battery powered devices. Set during the backdrop of hurricane Katrina in 2005, the film depicts the struggle of Nolan Hayes (Walker) who brings his pregnant wife Abigail to a hospital in New Orleans for the delivery of their daughter. Tragically, Abigail passes away following a complication during child birth and the premature baby is placed on a ventilator to keep her breathing.

The hospital is evacuated a few hours later when the hurricane hits, taking out the mains power supply. Subsequent flooding of the hospital takes out the backup generators, leaving the ventilator running on nothing but the onboard battery. By sheer luck, Nolan manages to find a hand-crank generator and connects this to the battery, only to see the monitor show "battery remaining03:00 minutes"

The rest of the film charts the trials and tribulations of Nolan as he tries to go about getting a message to rescue services, all the time having to contend with an ever diminishing battery capacity as well as dwindling food supplies and thieves.

Although this situation appears at first to be completely farfetched, in reality it may not be that implausible. The last few years have certainly seen a rise in the use of portable medical equipmentspecifically high powered devices such as acute ventilators and anaesthesia workstations where batteries are required to provide backup power in the event of a power outage.

Although increased portability gives doctors and paramedics the flexibility to transport patients, undertake more fieldwork and rely on auxiliary power when mains power fails, a lot is being demanded of the humble battery. Whilst it's not a big deal if your mobile phone dies mid-conversation, it's slightly more important that your life-support machine keeps going as any failure can, quite literally, mean the difference between life and death.

At Accutronics, we design and manufacture batteries and chargers for medical devices and have worked with many of medical device manufacturers to ensure their batteries are reliable, safe, cost effective and easy to use. So why did the battery in the film only have three minutes of charge and what could have been done to avoid this situation?

Here are our top five tips for getting the right battery for your medical device and to ensure it works when it is needed most:

1. Select the right chemistry
There are numerous battery technologies to choose from, each with their own specific performance traits. Established chemistry couples such as Nickel Cadmium have now mostly been excluded from the market due to environmental legislation and lead acid batteries are large and heavy making medical devices bulky and cumbersome.

Nickel Metal Hydride offers a cost effective solution with higher energy density but issues with heat evolution and a lack of technology investment make it a doubtful choice for the future.

It is Lithium ion which is proving itself to be the reliable chemistry of choice for new medical devices. 'Lithium ion' is the umbrella term for a battery technology that uses the intercalation of Lithium ions between a graphitic anode and a layered oxide cathode. The technology provides high energy density, excellent safety, low self-discharge and outstanding cycle life.

Through careful selection of cathode formulation and cell construction a wide range of Lithium ion cells have been developed that provide specific performance attributes, such as high discharge capability or high volumetric energy density.

2. Specify a 'smart battery'
To gain maximum performance from batteries in medical devices they should be made part of the power management system where battery, charger and host device communicate with each other to maximise safety, efficiency and performance. These so called 'smart batteries' only request charge when they need it, smart batteries charge more efficiently and use less power.

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