Battery chargers have been the norm for a long time. If you wanted a good flashlight you had to also purchase a charger. The convenience of having the charger built into the light is nothing new, high-end search flashlights have had built in chargers for a while. Recently, chargers are getting smaller in both size and cost. Thus chargers are being added to lights of all shapes and sizes. Having the charger built into the flashlight is more convenient for every type of buyer. From the hardcore flashlight collector to the mom who takes the doggies for walks. Rechargeable flashlights are great for everyone. Convenience is the name of the game here.
Not all charging ports are made the same, though. Nitecore favors the micro-USB port. Some have magnetic proprietary plugs like Klarus. Olight's Baton series and their accompanying docks are pretty great also. Look at these flashlights, and find the one which you find the most convenient and will fit your outlet and situation.