Techniques for determining whether a medical device will be able to deliver stimulation according to a particular program throughout a useable voltage range of a power source of the medical device are described. According to some examples, the medical device configures a DC to DC converter of the medical device in a specified output configuration and delivers electrical stimulation from the medical device according to a program while at the specified output configuration. Whether the medical device will be able to deliver stimulation according to the program when the power source is at a power source voltage level lower than a present voltage level used during therapy delivery is determined based on a value of a voltage drop across a regulator module determined while delivering the electrical stimulation according to the program. The determination for a program may be performed, as an example, when the program is created or modified.