# Hello, hello? My phone's almost dead...drat.

**Electricity and Magnetism**Level 2

Cell phone batteries are rated by their voltage and total ability to output current, usually in units of milliamperes \(\times\) hours, for which we use the abbreviation mA-h. If a battery has a value of \(1000~\mbox{mA-h}\), this means it can deliver \(1000~\mbox{mA}\) of current for one hour. The cell phone battery in this question has a voltage rating of \(3.7~\mbox{V}\) and current rating of \(1100~\mbox{mA-h}\). How much energy **in Joules** does the battery store when fully charged?

**Details and assumptions**

- Assume the voltage remains constant as the battery discharges. The voltage of real batteries decreases as they discharge, but we'll ignore that effect for simplicity.
- Hint: Try converting the rating to Amp-seconds and think how you could use that unit with Volts to get an energy.