Patch pump

A disposable module that can be coupled to a reusable module in order to form a pump for dispensing a medicament substance to a user in a metered manner in a coupled state, comprising a housing that encases the following components: a reservoir for receiving the substance to be dispensed; and at least one extensible cannula, which is fluidically connected to the reservoir either after being inserted or in a permanent manner. The disposable module may also comprise an electrical energy store, wherein the electrical energy necessary for the reusable module can be obtained both from the disposable module and also from a rechargeable battery in the reusable module, in order to ensure redundancy of the energy necessary for the reusable module.