As for battery capacity, basically it's exactly what it explains. Your battery capacity could be slightly lower then what the full capacity states. That's why it says typical next to 3900 mAh. And actual battery life depends on usage. For example, network, 5g will take more battery, weak signal can cause battery to drain quicker, then if you have a good signal. Depending on apps being used, some hit battery more then others. Other factors could be features you have turned on, how often the time you spend on you phone.
