Minecraft wiki entry for Minecart_with_Chest, associated text: The boost that minecarts with chests gain from powered rails is dependent on their load. For example, from a 1 powered rail starter track, an empty minecart with chest travels 64 blocks, but a full minecart with chest travels only 16 blocks (opposed to 80 blocks for an occupied normal minecart and 8 blocks for an empty normal minecart).