There are lots of good reasons to consider third-party alternatives when replacing or augmenting the rechargeable battery that comes with your digital camera. It is often cheaper to replace a dead battery with a cheaper name brand. A built-in charging port is another reason to kick Sony's own camera batteries to the curb.
Although most digital cameras will charge the inserted battery when connected to a power source, photographers usually rely on multiple batteries to get them through the day, which also means they're carrying around a proprietary charger so multiple batteries can be topped off as needed. When one goes missing, proprietary chargers can cause headaches.
The new UFZ 100 battery from Nitecore is designed to replace Sony's FP-Z 100 battery which is used in everything from the Sony a7 III to the a9 series. The Nitecore UFZ100 has a slightly less capacity than the Sony NP-FZ100, but it can be charged using a cable connected to almost any power source.