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Apple Watch battery life hits a snag

Posted: 09 Jan 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Apple? cobalt-oxide electrode? lithium-ion? Apple Watch? battery life?

The Apple Watch carries with a number of features that basically define the present status of wearable devices when it graces the market this year. What it doesn't deliver, however, is a sound battery-life. According to an executive, the Apple Watch would still need to be recharged everyday, just like most smartphones of today.

Mike Salas, VP of marketing at Ambiq Micro, discusses Apple's first wearable product and ways to improve it.

There are three basic ways to address battery life for a given device: choose a more advanced battery technology, improve charging, or increase efficiency. Let's have a look at each approach as it relates to the Apple Watch.

Apple Watch

Apple has not specified how the still evolving Apple Watch will be powered, but most likely it will use the currently leading battery technology for mobile devices, lithium-ion batteries with cobalt-oxide electrodes. Lithium-ion battery technology was developed in the 1970s, with commercialisation of the cobalt-oxide electrode material in 1991. Though this battery technology dwarfs its rivals in performance, it is nearing its theoretical limits. Newer battery concepts are in development, such as lithium-ion batteries with tin nano-crystal electrodes that are more effective at absorbing and releasing lithium ions than cobalt oxide electrodes, potentially doubling the energy capacity. However, these and other next-generation battery chemistries with even greater potential are a ways from being commercially available.

With a battery life of just a day or so, the Apple Watch needs a convenient charging routine to become a viable product. Inductive charging is the solution, with a small charging pad/connector that uses magnets to easily snap to the back of the Apple Watch. Once the watch and pad adhere to each other, energy is transferred wirelessly by magnetic induction from the transmitting coil in the charging pad to the receiving coil in the watch. No matter how simplified the process is though, a daily recharging requirement really puts a dent in the user experience.

On the efficiency front, the Apple Watch has a lot of opportunities to whittle down the power use because it is loaded with power hungry features. Besides being a very accurate watch that works with the iPhone to check its timekeeping against the definitive global time standard, the device includes a colour touchscreen, phone, messaging, email, Bluetooth connectivity for headphones, secure payment capability and an array of sensors for fitness tracking. A custom main processor is at the heart of the Apple Watch, with a design surely optimised and every operation surely scrutinised for low power consumption. Apple further elevates efficiency by employing an always-on motion co-processor to collect and keep all motion data on the device while the main processor sleeps.

After all this though, we are still talking about battery life for wearables in terms of days. Real breakthroughs will only come by taking on the battery life challenge at its most fundamental level, the IC architecture. One promising possibility is the use of sub-threshold voltage design techniques as pioneered by the authors' company.

- Mike Salas
??EE Times Europe

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