One aim of the project is to create a device that is portable, so we know we need a battery. But batteries have a tendency to be flat just at the time we need them most so we also want to make it possible to charge the battery via solar to give as much chance to send that crucial message as possible. There's a lot of design decisions to made - what type of battery? What capacity do we need? How can the battery be charged using solar? What are the trade offs between solar size and time to charge? Can we actually get any useful charge from a solar cell in Scotland?! As we work through these questions we'll update the logs to document our thought process and choices. Please feel free to offer any comments or advice.