Are there rules for charging?

Yes. Rule 1 for the lifetime: do not charge the battery to 100%. The charging percentage that is favorable for the life of the battery is between 20% and 80%. Often, a battery is not at all burdened; not even when a green or red light starts flashing. The smartphone only wants to warn you that some things may not be possible anymore. It is even worse to leave your fully charged device in the charger, as many of us do when we charge the battery overnight. For that small device, that only means stress, because the battery then constantly runs at full speed. When you pull the charger out of the socket, it feels like a kind of relief to the battery. “As if you can relax your muscles for a while after a heavy workout” (Source: battery university).