A storage system comprising a bin storing grid, a base of rails arranged above the bin storing grid, a remotely operated vehicle and a charging station assembly, wherein the charging station assembly is for charging a plurality of power sources (106a-g) and comprises a charging station support fixing the charging station assembly on the base; characterised by further comprising: a plurality of charging stations (106a'-h'), each charging station (106a'-h') arranged at a different vertical position and comprising charging means for charging one of the plurality of power sources (106a-h); and a power source transport device enabling relocation of any one of the power sources (106a-h) between an operational position on the remotely operated vehicle and a charging position in or at one of the plurality of charging stations (106a'-h'); wherein the power source transport device comprises a power source lift vertically movable between - a first vertical position in line with, or near in line with, a power source position on the remotely operated vehicle when the remotely operated vehicle is situated on the base and - a second vertical position in line with, or near in line with, any one of the plurality of charging stations (106a'-h'), - the first vertical position at a lower level than the second vertical position, and the power source lift comprises power source connection means (102a,102b) comprising a horizontally movable support and at least one connecting device fixed to the horizontally movable support for reversibly disconnecting the power source (106a-h) from its operational position on the remotely operated vehicle during use; and the second vertical position is at a level above an uppermost level of the remotely operated vehicle, such that the remotely operated vehicle is positioned below the plurality of charging stations (106a'-h') during the reversible disconnection of one of the plurality of power sources (106a-h) from its operational position on the remotely operated vehicle. a plurality of charging stations (106a'-h'), each charging station (106a'-h') arranged at a different vertical position and comprising charging means for charging one of the plurality of power sources (106a-h); and a power source transport device enabling relocation of any one of the power sources (106a-h) between an operational position on the remotely operated vehicle and a charging position in or at one of the plurality of charging stations (106a'-h'); wherein the power source transport device comprises a power source lift vertically movable between - a first vertical position in line with, or near in line with, a power source position on the remotely operated vehicle when the remotely operated vehicle is situated on the base and - a second vertical position in line with, or near in line with, any one of the plurality of charging stations (106a'-h'), - the first vertical position at a lower level than the second vertical position, and the power source lift comprises power source connection means (102a,102b) comprising a horizontally movable support and at least one connecting device fixed to the horizontally movable support for reversibly disconnecting the power source (106a-h) from its operational position on the remotely operated vehicle during use; and the power source transport device comprises a power source lift vertically movable between - a first vertical position in line with, or near in line with, a power source position on the remotely operated vehicle when the remotely operated vehicle is situated on the base and - a second vertical position in line with, or near in line with, any one of the plurality of charging stations (106a'-h'), - the first vertical position at a lower level than the second vertical position, and - a first vertical position in line with, or near in line with, a power source position on the remotely operated vehicle when the remotely operated vehicle is situated on the base and - a second vertical position in line with, or near in line with, any one of the plurality of charging stations (106a'-h'), - the first vertical position at a lower level than the second vertical position, and the power source lift comprises power source connection means (102a,102b) comprising a horizontally movable support and at least one connecting device fixed to the horizontally movable support for reversibly disconnecting the power source (106a-h) from its operational position on the remotely operated vehicle during use; and the second vertical position is at a level above an uppermost level of the remotely operated vehicle, such that the remotely operated vehicle is positioned below the plurality of charging stations (106a'-h') during the reversible disconnection of one of the plurality of power sources (106a-h) from its operational position on the remotely operated vehicle.