What is draining the battery of a 2004 Pontiac Bonneville
Battery is constantly draining for no apparent reason?
It's caused by an electrical short. You or your mechanic will have to probe each and every circuit to determine which circuit it is, then find the problem on the circuit by then inspecting and probing the wiring and switches. Most times it is a cut, worn wire insulation and or corrosion.
Search " parasitic drain " Do you have something plugged into the cigarette lighter ?