I don't like the car analogies because I don't think they fit. But following along with it. No, an ECM doesn't make power and neither does a charger. The power comes from the alternator, PV panels, or the AC outlet/power company. A charger adjusts the voltage from the power source, and an ECM adjusts power output of the engine.
The charger converts voltage from the power source to a voltage that given the internal resistance of the battery will not cause excessive current. Think of the most-simple charger, a step-down transformer and rectifier bridge. There is no current limiting or control there at all, only a change in voltage. And in their most basic sense, that is what all chargers do, change the incoming voltage to the correct voltage for the battery to charge at the correct current. I call them a voltage device, because that is what they provide. Regardless of the load or current that flows, they attempt to provide the correct voltage to the battery for proper charging.
Consider a current device, like a driver for a fluorescent light or an LED. For either of these, what matters is the current. A fluorescent lamp will have a massive drop in resistance as it illuminates and warms up, and as this happens, current needs to be kept constant. If a constant voltage is used then the current would increase as the lamp's resistance decreased, and it would burn out. So, a resistance in the driver is changed so that the current stays constant, and the voltage be whatever it needs to be.
The charger provides a regulated voltage, and the fluorescent driver provides a regulated current.
