USB to 4.2 volts can be used with wall or car phone charger for the Bubs Daddy 2, 4, battery units and Frabill replacement aerators.
You can charge your batteries and run the unit at the same time. A good 2 amp or larger USB charge cube or 12v to USB cigarette plug is recommended.
It is also recommended to charge your batteries using an external Smart Charger on occasion to ensure they are maintained at top performance.