These devices now auto-charge the batteries automatically i.e when the battery drops below its nominal 3.3V charge it is automatically topped up. This charging scheme can be manually turned on or off by a push button.
The charging will now operate form a 5V power supply. This leaves the option of powering the battery charger from a spare USB port separate to the one used . A suitable USB cable is required with USB A male to 2.1mm plug.