Whoop’s new fitness tracker is better thanks to a battery breakthrough

Fitness company Whoop has a new tracker that squishes five LEDs, four photodiodes, a pulse oximeter, skin temperature sensor, and more into a package that is 33 percent smaller than its predecessor — all while still offering five days of battery life. But a particular change to the tracker’s battery chemistry is one of the biggest reasons Whoop was able to do all this in the first place.

The change was pioneered by a Silicon Valley company called Sila Nanotechnologies, which was co-founded in 2011 by Gene Berdichevsky, one of Tesla’s earliest employees. And it’s one that, if it scales up, could help break some of the biggest limitations currently facing lithium-ion technology.

On paper, it’s a simple change: the battery’s anode is now…

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