A replaceable fluid container for an engine or a vehicle, comprising: a fluid reservoir, at least one fluid port adapted to couple with a fluid circulation system; and an actuator, configured to be operated between a first condition and a second condition, wherein the actuator is configured, in the first condition, to enable the fluid container to be inserted into and/or held in a dock, in a seated but undocked condition, and inhibit docking of the fluid container to the dock; and wherein the actuator is further configured, when operated from the first condition to the second condition with the fluid container being in the seated but undocked condition, to enable the fluid container to dock in an engaged condition with the dock, associated docks and associated methods of supplying a fluid to a vehicle or an engine and of decoupling a fluid container from a fluid circulation system of a vehicle or an engine.