Yeah iphones are pretty small. I seem to remember some of my Sammys and Motos having in the 9-12 range. 37 might actually be approaching some small netbooks.

The capacity for energy storage is volts * amps over time. So a 10 amp hour battery at 3.7v holds less energy than a 10 amp hour battery at 12v. Together it makes watt-hours. That's the best way to measure storage capacity.