As batteries get smaller to accommodate the trend for smaller and lighter devices, we begin to see some trade-offs. The Lithium-ion (Li-ion) cells that make up the majority these batteries have a limited gravimetric and volumetric energy density and subsequently, wearable devices inevitably suffer from inadequate runtime. If your smart phone runs out of juice then it is inconvenient, but if the same device is monitoring your health then it is far more concerning.
This reduction in battery quality is a real concern. The lifespan of a rechargeable consumer Li-ion battery averages around 300-500 charge cycles before its capacity drops to an unacceptable level. Because medical devices outlive their batteries they tend to use removable rather than embedded batteries.
To combat this problem for wearables, Accutronics has already developed a credit-card sized battery for use in wearable medical devices. Today, these batteries are being used to power devices that are worn by patients, monitoring their health or providing medication when the patient requires it. Being removable means the battery can be swapped for another when charging is required and the device does not need to be returned to the manufacturer for a battery replacement when the original set of batteries reach end of life.
Although battery quality is a major problem for consumer medical devices, there are deeper concerns when it comes to the manufacture, testing and regulation of the industry as a whole. Because this industry has seen rapid growth over the last three years, many far east manufacturers have taken shortcuts by producing gray market knock-offs, and sometimes outright illegal batteries, that lack the necessary protection circuits that are needed to prevent Li-ion batteries from overcharging, overheating or becoming unstable and potentially catching fire.