Techniques for determining whether a medical device will be able to deliver stimulation according to a particular program throughout a voltage range of a power source of the medical device are described. According to some examples, the medical device simulates a power source voltage level lower than a present voltage level of the power source, and delivers stimulation according to the program while simulating the lower power source voltage level. Whether medical device will be able to deliver stimulation according to the program when the power source is actually at the lower voltage level is determined based on an electrical parameter measured during the delivery of stimulation while simulating the lower voltage level. The simulation and determination for a program may be performed, as an example, when the program is created or modified.