Trade-offs in smartwatch design


Why top smartwatches struggle to reach a one day battery life and what we can do about it.

Smartwatches are amongst the most widespread wearable technology nowadays and perhaps one of the most challenging to design. Their proximity to the human body and position around a highly visible area poses unique design challenges that tech brands are still trying to solve.

When designing smartwatches, in fact, designers and engineers need to find a trade-off between three main opposing factors: Comfort, Performance and Battery life. While comfort is non-negotiable and performance is a key differentiator, battery life is often the factor that gets compromised, with leading smartwatches struggling to reach a one day battery life in normal usage.

In this article we will analyse how these three factors are driving the smartwatch market and will present possible ways to improve battery life and to minimise its negative impact on people’s lives.

Comfort vs Performance vs battery life: a constant battle.

Tech brands are caught between opposing factors that prevents them from creating the perfect smartwatch: Comfort, Performance  and Battery life.

Comfort. The analog watches we have been using for centuries, that smartwatches are designed to replace, set very high expectations in all of us. We expect smartwatches to be small, thin and light, to feel good on the wrist all day long, not to get caught under long sleeves, to look great with different outfits, to be customisable and fashionable.

Although in the early ages of smartwatches (early 2010’s) we have seen wild explorations with very capable but huge-sized wearables that looked like smartphones strapped to a wrist, the market has now made it clear that comfort should be a sine qua non condition for smartwatches to be adopted.

Performance. Nowadays top smartwatches as a minimum must have LTE connectivity, GPS activity tracking, NFC, smart assistant support, ECG reading, a large always-on touch user interface and should be compatible with the most popular third party apps.

As the smartwatches category is maturing, brands are in a constant rush to add the newest cool feature to differentiate, demanding an always increasing amount of space, energy and processing power.

Battery life.  Li-ion battery technology powers the majority of modern tech, from  laptops, to smartphones, e-mobility and wearables, including smartwatches. As the Energy Density, described as the amount of energy a battery stores per unit volume, is a constant (about 690 Wh/L),  it is not possible to increase the stored energy of a battery without increasing its size.

As a result, most smartwatches nowadays mount a battery of  about 350-450mAh, that comes in an approximately 40x30x4mm package, a volume that fits well into a common wrist watch form factor, but is only able to power a watch for about one day in normal conditions.

Smartwatches categories reflect this tension

When designing a smartwatch, design and engineers need to find a trade-off between these three factors, giving more importance to some while compromising on others. As a result, the smartwatch market can be mapped into three main categories each ‘trading-off’ one factor over the other two.

Fitness watches (good comfort, good battery life, limited performance)

Fitness watches  are generally slim and light, with a simple user interface, and their functionalities are mostly oriented on tracking fitness and lifestyle data.

They typically offer a good battery life (a few days to a week) and are comfortable to wear, however they lack advanced features that top smartwatches offer.

EXAMPLES: Fitbit Versa / Sense

Smart watches (good comfort, good performance, poor battery life)

Smartwatches are generally comfortable enough to wear, and integrate a variety of smart features such as managing messaging and calls, smart assistant support, always on display and compatibility with third party apps. However, all these features come with a price, as they struggle to reach a one day battery life in normal conditions.

EXAMPLES: Apple Watch 8, Galaxy Watch 5, Pixel Watch

Pro’ Smart watches (poor comfort, good performance, good battery life)

Professional smartwatches are targeted to high profile users that use their smartwatch in extreme conditions (typically athletes, explorers etc.). They integrate state of the art functionalities and feature more capable batteries to support users for longer sessions, however they are generally bulkier and less comfortable to wear.

EXAMPLES:Apple Watch Ultra, Galaxy Watch 5 Pro

“But, what if we didn’t have to compromise? How to create a smartwatch with good comfort, high performance and great battery life?”

Following this analysis it might now be apparent how battery life represents the chilles’ heel of smartwatches design. To compensate the limitations of Li-ion technology, smartwatch brands have adopted a variety of ways to improve battery life: through software optimisation (see Apple and Huawei proprietary watch OS), by integrating more energy saving components (see Apple watch S chips), by using for instance hybrid tech displays (see Ticwatch Pro 3 dual display). These improvements however, although honourable have been rather incremental with improvements on battery life in the range of 10-20% (without limiting the watch functionalities).

Only with the advent of a new reliable and cost efficient battery technology able to pack more energy into a smaller package, will smartwatches reach the battery life we all hope for.

Until then, tech brands will keep struggling in finding a trade-off between comfort, performance and battery life in order to create a smartwatch that appeals to people.

“If battery life cannot be radically enhanced, how could we then minimise its negative impact on people’s lives?”

Smartwatches typical charging experience mimics the one of smartphones, without really considering smartwatches peculiarities.

As all wearables, in fact, smartwatches are designed to operate directly on the human body, in order to collect precious data and eventually be useful for people.

However all smartwatches nowadays need to be removed from the wrist in order to recharge as they feature either contact pins or a wireless charging coil in the bottom face of the watch.

01. Remove the watch from the wrist
02. Connect it to the charger
03. Monitor the charging status as the watch is charging
04. Unplug the watch and put it back on the wrist

As a result, while recharging, the watch does not do what it is designed for: tracking health and lifestyle data, as well as providing notifications on the wrist. It is as if our smartphone while charging wouldn’t be able to receive and make phone calls, browse the internet or connect to social media. Sounds absurd, isn’t it?

Recharging a smartwatch might take one to a few hours. Moreover it is not uncommon for people to leave the watch on the charger even after it is fully charged, because they forget, or because they are sleeping, or because they need to leave for whatever reason, resulting in a ton of precious data not being collected.

What if you could wear your smartwatch 24/7 recharging it directly at your wrist?