Not as concerned about the cellphone as my camera. The cellphone goes into airplane mode or is turned off to conserve battery. I do that a lot because I’m antisocial and prefer to not answer the phone when I’m out and about. The camera OTOH uses power faster than you’d think, but can recharge its battery if given a USB power source. 3400 mAh does a good job charging the 1400 mAh battery in my small camera or the 1900 mAh battery in my larger full frame. I really miss my old manual film camera. Recently picked up a spare for the small camera since I use it more, but a USB power source you can drop in your pocket is always useful.