Replaceable fluid containers for engines, such as those comprising at least one fluid port adapted to couple with a fluid circulation system of the engine when the replaceable container is coupled to a dock, a data provider configured to provide analog data characteristic of at least one of the fluid and the container, an analog-to-digital converter configured to convert analog data from the data provider into digitized data, and an interface configured to provide the digitized data unprocessed to an interface of the dock for supply to a processor configured to process the unprocessed digitized data to provide an indication of a property of at least one of the fluid and the container, related replaceable fluid containers for engines and associated methods of determining a property of a fluid in a replaceable fluid container for an engine.