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5 tips on how to pick the right battery for medical devices

27 Mar 2015  | Neil Oliver

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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 that 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.

Smart batteries maximise the runtime per discharge cycle because they tell their host device when to shut down based on a highly accurate remaining capacity prediction. This method is superior to dumb systems that use a fixed voltage cut-off. Host medical systems that use smart battery technology can provide accurate, meaningful runtime information to users, of vital importance in a medical environment where power failure is not an option.

Smart batteries constantly track their own capacity whether they are being charged, discharged or stored. Their battery fuel gauges use correction factors to adjust for changes in temperature, charge rate and discharge rate together with further modifications as the battery ages. Properly designed and calibrated smart batteries can predict their capacity to within 1 per cent, which means that medical device manufacturers can provide users with a device runtime figure they can trust.

3. Size the battery correctly

It is important that the battery inside a medical device is correctly sized for the job it needs to do. Users that think their battery may not power the device for long enough may suffer from runtime anxiety and refuse to use the device on battery power or never move far away from an AC power outlet.

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