: this thread is now at 106 posts, since your original post on January 10, 2020. You have received excellent advice which you have apparently decided to ignore. Instead you have been re-posting the same questions repeatedly. What more, exactly, do you expect to learn here? Are you aware that your "plasma pen" is a dangerous piece of "snake oil" merchandise that can result in serious injury and/or infection of the "treated" sites?
Are you aware that none of us here has any idea what battery, or battery charging circuit, is inside your device? No body here knows what the "bars" mean on the plasma pen display. Three bars does NOT mean the battery is 100% charged, as you have assumed. It only means the battery is charged more than it is when two bars, or one bar, or no bar is displayed. Similarly, two bars means NOTHING with regard to how much the battery is charged. Two bars just means the battery is charged LESS than three bars and MORE than one bar or no bar. Finally, one bar means NOTHING with regard to how much the battery is charged. One bar means the battery is charged LESS than two bars or three bars but MORE than NO bars. No bars probably (but not certain of this) means the battery is dead.
You have said that you cannot access the internal battery, or at the very least do not know how to do so. That means you cannot make any voltage measurements on the battery terminals, which means you cannot determine the charge state of the battery. If you cannot determine the charge state of the battery, then you have no way to determine when to charge it, how much to charge it, or how often to charge it for maximum life. None of us here at Electronics Point can provide you with anymore useful suggestions. Please go troll another forum for "answers" to your interminable questions. There are no further answers available here.