Dead battery, cigarette charger, and horn chirp

[JFP in PA]

Originally Posted by kjc2050

So my question is, if this works with no battery, why wouldn't it work with a dead battery?

Because a dead or dying battery preferentially sucks up all the energy put into the system like a giant sponge. Eventually, when the battery develops enough reserve, things will start working, but not until the battery gets what it needs first. And if the battery is really in bad shape, the lighter circuit cannot deliver the necessary current to bring the battery back up. So, in a way, you would be better off if the battery was not there............