I didn't realize that coin cells were so limited. I'm glad I asked this now. I originally had suggested that my wife use a running tracker app that she can get for her android phone but she doesn't want to have to carry the phone on a run because it is too big. What I plan to make for her will be a lightweight box that is slightly bigger than an arduino nano that she can wear on a lanyard around her neck. I think a battery such as the ones that come in those tiny remote controlled helicopters may be appropriate. Is there a way to predict how long a battery with a certain capacity will last if I know the current draw of each device that it will be powering?