Who doesn't fear running out of battery? Everybody does.
Current apps that show you where friends are have a significant impact on battery. This is because they use GPS to figure out where you are and Internet to download your friends locations, and this is battery unfriendly. We don't like that.
Nowy Friends is kind on your battery, because it only uses Bluetooth Low Energy to detect your nearby friends. There is no need to worry about battery. You can leave Nowy Friends running all day long.