Charging a cell phone with a 6-volt battery can be done, but it depends on the power requirement of the phone. Cell phones come with a wide range of power requirements. Some phones use 3.6 volts, 5.0 volts or more. A 6-volt battery is best suited for a cell phone requiring 5.0 volts. This minimizes the number of extra electronic components needed to connect the battery and the cell phone. Use the old cell phone charger for parts.

How to Charge a Cell Phone From a 6 Volt Battery  4 Steps  - 62