Sunnytech 10pcs 0.16w 4v Round Shape Mini Solar Panel Module Solar System Solar Epoxy Cell Charger DIY mini solar panel Build your DIY powered models/solar toys / solar displays Size: diameter 81.3mm. Charging small DC batteries When the voltage of your solar panel don't satisfy your storage battery, you can take two or more same solar panels together in serices. Such as,two 5.5v solar panel take together in serices, so its voltage is 11V. when the voltage of solar panel satisfy your storage battery. In order to Speed up the rate of charge, you can take two or more same solar panel together parallel connection. It can be used for teaching purpose. Many of our customers comes from school,colleague,etc.