Methods of providing payment for use of a medical device on a per-treatment session basis are disclosed. The methods include downloading treatment credits to the device linked to a customer account and activating the medical device when the number of available treatment credits is greater the one. The number of treatment credits downloaded to the device is based on at least one of a credit limit provided to the customer account and a number of prepaid treatment credits purchased by the customer. In other embodiments, the medical device monitors the number of treatment sessions performed and activates the device only when a customer's account is current.