It's a helpless feeling, holding a dead phone.
But one start-up is devoting a lot of energy to solving this perennial problem, and it's putting you in charge.
"We were all active people, so we thought--why can't we use the calories we burn while running, walking, biking, etc., to recharge our smartphones?" Tejas Shastry told CNBC.
So Shastry, along with co-founders Alex Smith and Mike Geier, created AMPY MOVE, a pocket-size wearable motion-charger. It's a lightweight device that transforms kinetic energy generated from everyday movement into battery power. The more you move, the more power you get.
"Your movement is your power," Shastry said.
According to the start-up, one hour of exercise creates as much as one hour of battery life. But if you're not actively using the phone, that one hour of exercise translates to five hours of standby power. So users have power when they actually need it. AMPY may also be plugged into the wall.
The cofounders named AMPY MOVE after "amp", a unit of electric current. The device itself retails for $99.
The start-up also plans to release an app that tracks the amount of energy a user generates everyday. A feature that AMPY expects will get users to "compete" with friends.
Patrick Chung is a founding partner at venture firm, Xfund. He wondered if the start-up is branding itself as a battery company or as "the holy grail of social fitness companies."
"We actually think of ourselves as defining a sort of new product category which is wearable motion chargers," said Smith.
According to Shastry other kinetic and renewable chargers on the market "are all far too big and bulky to ever fit into your life." The start-up's proprietary inductor technology allows AMPY to scale down to a wearable size. And the founders' future plans involve licensing and co-developing with outside companies to get AMPY technology into other wearable devices.
Angel investor Nat Burgess, who is president of Corum Group, said his worry is how the start-up would protect itself against competitors such as Samsung, Google, Microsoft and Apple.
Shastry said, he has confidence in the start-up's patented technology. He also said AMPY is always devising new ways to protect its technology.
Since its launch in March 2014, AMPY has raised approximately $900K in funding via competitions as well as crowdfunding.
The start-up boasts more than $15,000 in revenue each month since its Kickstarter campaign in November 2014. Shastry expects AMPY to be profitable within a year.
The start-up is headquartered in Evanston, Illinois, and has six full-time employees.