Generally you should be able to use your phone with Pruvan all day, if you charge between jobs and your device is less than 2 years old.
If you are a high volume user you may need a external battery pack for you phone.
Pruvan recommends the following hi capacity external battery. This can charge your phone from your pocket. It is basically 5 or 10 charges in your pocket. You will need to charge both your phone and external battery pack each evening.