If you are planning to store your device for a long period of time, the best thing is to partially charge the battery and then store it. By storing in the discharged state, you may face problems with recharging. Again, storage of a battery in completely charged state can reduce its life span. https://goo.gl/ybNwx4
If a capacitor marked D.C. is used as an A.C. capacitor, the maximum working voltage is limited by the heat produced or by discharges. The maximum working voltage converted to AC voltage depends on different types of the capacitors. For more details, please contact us.