During the day, Spark batteries store the solar power that you don't use. You can use it to power electronic devices, like lights or a TV – four lights can run for up to 8 hours on one. When batteries are connected, they can store even more power. Each battery has 2 USB ports in order to connect smaller electronic devices like a phone or clippers. They also. The Screen shows the current battery level and how many days are left until the next payment is due. Use the buttons to see more data, such as how much time is left before a battery runs out. Batteries can be paid for individually, to help you cut back or power up when you need to. Adding credit has never been easier with the Screen. You.