Wednesday 6 May 2015

Top five tips for specifying batteries in medical devices

At Accutronics, we work with the world's leading medical device manufacturers to develop class leading batteries and chargers. I am often asked "what should we consider when specifying a new battery? Well here are my top five tips to get you going.
 

Tip #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 that use them 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. 
 

Tip #2. 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 run-time anxiety and refuse to use the device on battery power or never move far away from an AC power outlet. Medical device designers should think carefully about their device’s power budget when running on battery power and then factor in the effect of battery ageing, ambient temperature before deciding on a battery energy rating. If space is at a premium and long run-time is required then hot-swappable batteries may be considered to lengthen the operation of a medical device.
 

Tip #3. 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 run-time 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 run-time 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% which means that medical device manufacturers can provide users with a device run-time figure they can trust.
 

Tip #4. Get certified

Medical devices that are certified to IEC60601-1 must have their batteries certified to IEC62133 which is a safety standard for portable batteries. If the product is to be sold in the USA then the FDA also recommend batteries are certified to another safety standard - UL2054. For batteries using Lithium ion cell technology then mandatory transportation testing must be performed to provide the battery is safe for transport. A good battery integrator will manage this certification process seamlessly, ensuring worldwide market compliance. 
 

Tip #5. Ensure it is reliable and safe.

Without the battery, any portable medical device becomes an expensive liability. It is the battery that is the heart of machine and it must work when needed and never pose a risk to its environment. A good battery integrator will ensure the battery contains ‘nested’ layers of safety that include its cell selection, mechanical design, passive protection and active electronic protection elements.
 
Battery integrators such as Accutronics that are certified to ISO13485 have the expertise and processes in place to ensure risk assessments, design reviews and performance verification is conducted diligently and thoroughly.
 
If you wish to discuss any of the points raised above or if you want to discuss your plans for a new battery development then please drop me an email.
 
Neil Oliver
Technical Marketing Manager
Accutronics Ltd

 

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