When charging your battery at, suppose 70% many of the electrons get over charged, by the current, but at 5% when the current come in the electrons go for the charge and it can even rejuvenate dead electrons. So for best results you should always drain your battery under 20% then charge it up as much as you can. If you can only end up charging to, lets say 60% you should wait until it drain under 20% to charge again. Although there won’t be a significant difference in the battery if you happen to charge it at over 20% once in a while.