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The medical world is matching the trend toward greater mobility via increasing lifesaving and monitoring abilities in the field, as well as in fixed-base health facilities. There is, however, added urgency when it comes to delivering reliable portable devices when human lives hang in the balance. After all, if a consumer’s portable heart-monitoring device or infusion pump stops working because of a dead battery, the dilemma is far more serious than a cell phone failure.

Not long ago, medical professionals were unable to take life-saving equipment out into the field. Today, a wide variety of monitoring devices, ultrasound equipment and infusion pumps are being taken to, and stored at, remote locations, even battlefields. Portable equipment is more mobile than ever thanks to the implementation of technologies such as lithium ion batteries. Defibrillators, for example, that used to weigh 50 lbs. are lighter, more compact, and user friendly.

Patient mobility is also increasingly important. Today’s patients may go from X-ray to ICU, from ambulance to emergency room, or from hospital to hospital with an ambulance ride in between. Portable medical devices must, after all, be truly portable to be optimal.

Another phenomenon seen more often is the proliferation of portable home-use devices. Li-ion technology may be a good choice for such devices for its excellent reliability and “smart-battery” attributes that will be elaborated.

The most recent trend toward battery power is in the surgical suite. Surgeons are demanding electric devices over manual or pneumatic power, but tethered devices are unwieldy in an already crowded operating room. New Li-ion technology provides the high power necessary for surgical devices and while design for sterility presents a challenge, it can be overcome with careful engineering.

Why switch?

There are compelling reasons why cellular phone, computer, and power tool makers have progressed from nickel-cadmium (Ni-Cd) to nickel metal hydride (NiMH) to Li-ion or Li-polymer technologies in recent years, and similar reasons are moving increasing numbers of medical device manufacturers to these chemistries.

The first advantage battery makers and pack suppliers often mention with Li-ion technology is the pronounced energy density increase. For their size and weight Li-ion cells store and deliver more energy than other rechargeable batteries, making it possible to shrink the size and increase the convenience of portable products.

With Li-ion you are often able to get the same amount of power as a Ni-Cd or NiMH solution with fewer cells. Your medical end users will be the first to tell you that the “mobility” of your device is greater when there’s less bulk to carry or cart around. Meanwhile, shrinking the battery pack compartment may also allow for designing additional device capabilities in the same product.

Energy density must be measured both volumetrically (by size, in liters) and gravimetrically (by weight, in grams). Li-ion technology is now up to almost 600 watt-hours per liter, and 500 watthours per gram. In other words, Li-ion is able to deliver more power with a smaller footprint and less weight. Here is a comparison chart for the various energy densities of portable cell technologies:

Li-ion’s energy density is primarily attributed to the higher operating voltages than other rechargeables, typically about 3.7 volts, versus the 1.2 volts for Ni-Cd or NiMH. This voltage increase means a single cell can often be used rather than the multiple cells required when using older technology batteries. This factor not only leads to a smaller footprint, but also often brings the total solution cost to almost equal amounts. Sealed lead, which is a 2V cell chemistry, is generally packaged in either 6V or 12V configurations, which can mean wasted power if the end unit operates on lower voltage.

Weight savings

A noticeable weight savings is a major bonus of using Li-ion battery technology. Li-ion cells not only weigh less than competing battery technologies, the ability to use fewer cells for the same power delivery also means less weight and less wasted power.