Abstract: A medication fluid delivery device and methods are provided with the delivery device having a dispensing unit and a drive unit that are attachable together. The dispensing unit includes a dispenser for delivering medication fluid to a user and a reservoir configured to be filled with a variable amount of medication fluid received from a medication fluid injector. The drive unit includes a control unit that controls the drive unit and causes medication fluid in the reservoir to be pumped through the dispenser and includes a registration mechanism configured to act with the dispensing unit to determine a state the reservoir including an initial level of the filled reservoir.