Due to the ever-growing uptake in the use of electronic wearable devices by healthcare professionals and patients alike, the number of applications and functions is also increasing. Therefore, the old approach of one-battery-fits-all can no longer apply, as batteries must meet the size and power requirements of each device. Here, Robert Brown, Marketing Executive at battery manufacturer Ultralife, explores some of the different types of wearable devices used in healthcare, the current challenges to powering these devices and the solutions that are currently available.
Types of wearable MedTech
Probably the most common and well-known wearable devices in healthcare are used for patient monitoring. There are two types: remote patient monitoring where data is collected and sent to the healthcare provider for diagnosis, and monitoring where data is accessed solely by patients who are self-managing long-term conditions (such as glucose monitoring for those living with diabetes).
In both instances, battery-powered sensors are housed inside the patient-worn device, and battery-powered RF transmitters relay the data they record back to the healthcare provider or directly to the patient. The patient-worn device may be shaped like a watch and go around the arm, or be an adhesive patch affixed to the arm, chest, face, neck, or leg.
Additionally, there are adhesive patches that can dispense medication, such as insulin to treat diabetes. These patches use electronics to run a pump that controls drug delivery in doses.
There are also devices that do not attach to the skin but hang on a cord around the neck, such as medication reminder devices. Some of these devices are pill containers that have a timer at the top that must be set after each dose is taken. Others have a radio-controlled clock that automatically sets the current time and can be pre-programmed to alert the wearer multiple times a day.
Current challenges
In all cases, if devices are tampered with or batteries removed, this could prevent patients from getting the data, medication or alerts they need. There is also the worry that patients could remove the wearable device if it gets too uncomfortable, with the same consequences. A wearable device is more likely to be uncomfortable if it is thick and heavy. For example, a watch may dig deeper into the skin or a patch may protrude too much and get caught on clothing when the wearer is getting dressed. However, although the device must be as small and light as possible, it still needs to offer high performance and reliability.
Unlike the first battery-powered wearable devices that had a continuously low power output, like electric wrist watches in the 50s where coin cells were well-suited, modern wearable healthcare devices may lie dormant and then use high pulses of data when they are required to perform their function. For example, patient monitoring devices use RF transmitters or motors that require high bursts of energy to transmit data or deliver drugs. For medication reminder devices, a high pulse of energy is required to sound alerts at the correct times.
Solutions
To prevent battery removal, batteries can be embedded for the lifetime of the device, so long as they perform well throughout that time. Non-rechargeable batteries have a longer service life than rechargeable alternatives, making them ideal for fitting into devices. However, some non-rechargeable batteries are longer lasting than others, depending on the amount of energy they can store (capacity) and the rate at which they lose energy during storage (self-discharge). The maximum capacity for a coin cell is 1000mAh but Ultralife manufacture Thin Cells® that have capacities up to 1900mAh, with an equally low level of self-discharge between 1% and 2% after one year of storage at +20°C.
When it comes to performance, some chemistries like alkaline suffer from drops in voltage during use. Lithium Manganese Dioxide does not have this problem and offers a flat discharge curve, which means higher power and more energy for the whole battery life.
Another solution is to make the device more comfortable for the wearer, by ensuring it is as thin and light as possible, whilst also meeting the power demands of the device. Coin cells are manufactured in a small number of standard sizes and weights, but Thin Cells® are much more customizable. In 2021, Ultralife expanded its range of pre-engineered Thin Cell® batteries to include the thinnest model yet, measuring 1.1mm thick, offering a weight of 4.0g, a maximum continuous discharge current of 50mA, and an energy rating of 1.14Wh. There are eight other variations available, offering different thicknesses from 1.3mm up to 6.2mm, weights from 1.1g to 15.7g, maximum continuous discharge currents up to 500mA, and energy ratings up to 5.7Wh.
In addition to the pre-engineered cells, Ultralife can also manufacture custom sizes based on customer requirements. Once a design engineer has determined the power requirements of their device, dimensions can be inputted into Ultralife’s online Thin Cell® calculator to show the estimated capacity, maximum continuous discharge and maximum pulse discharge that will result. This allows design engineers to work out the smallest size cell they can have that meets their power needs.
Finally, low resistance current collectors can be used to help batteries serve applications that require high bursts of energy, such as those that need to sound an alert, transmit health data, or dispense medication. Ultralife’s Thin Cells® have these and outperform Coin Cells at higher discharge rates. In devices where high power is needed, such as drug delivery systems, Ultralife Thin Cells® have a continuous discharge current up to ten times that of a coin cell of the same capacity.
Although medical wearable devices serve different functions, such as sounding alerts, gathering health data, or drug delivery, they share challenges such as the need to strike the right balance between size and power. Research is always taking place towards producing the next generation of battery technology, so the future of wearable MedTech batteries is unknown but, for now, Thin Cell® batteries play a vital role in overcoming these challenges, as they are customizable and long-lasting.
To learn more about the range of Thin Cells® from Ultralife, please fill out an inquiry form or call +1 (315) 332-7100.
