Fluid cartridges and fluid amount detection systems

There is provided a fluid cartridge including a fluid container. The fluid container includes a fluid chamber configured to store a fluid and an fluid outlet passage configured to supply a fluid therethrough from an interior of the fluid chamber to an exterior of the fluid chamber. The fluid container further includes a first flexible sheet portion and a second flexible sheet portion. The first flexible sheet portion has a first surface facing an interior of the fluid container and a second surface opposite the first surface and facing an exterior of the fluid container, wherein the first flexible sheet portion is configured to deform when a pressure difference (P2-P1) between a pressure (P1) acting on the first surface and a pressure (P2) acting on the second surface becomes equal to or greater than a first value. The second flexible sheet portion has a third surface facing the interior of the fluid container and a fourth surface opposite the third surface and facing the exterior of the fluid container, wherein the second flexible film is configured to deform when a pressure difference (P4-P3) between a pressure (P3) acting on the third surface and a pressure (P4) acting on the fourth surface becomes equal to or greater than a second value. The second value is greater than the first value.