You can charge 1-2-3-4 battery's at one time as long as you provide 1amp per battery for fastest charge. I think this is a TP4056 Lithium cell charger for each cell. This is not a exact duplicate of the circuit, all minus side have to be independent, no common grounds. From bridge + to + on li-po charger board & - from bridge to - on li-po charger board, than hook to battery's as shown without common ground as drawing shows. The bridge or a single diode can be used to keep grounds isolated.
