What is does a cell phone go straight to voicemail when the battery has died?

When a cell phone battery has died, it cannot actively receive or make calls. Therefore, if someone tries to call a phone that has a dead battery, the call will not be answered and will go straight to voicemail. It is important to note that if the phone has enough battery for the call to ring but dies during the call, the call will be disconnected rather than going straight to voicemail.