Cars are primitive things. Sure, newer models have more features, with bright, fancy displays and microprocessor-controlled ignitions. But at its heart, a car is simply a series of controlled explosions, and everything around it to harness them. More to the point, certain systems of cars haven't advanced much in the last 50 years. The largest innovation in car batteries during this time appears to be the addition of a carrying handle. And yet, the charging system is one of the most misunderstood parts of a car.
Perhaps this is because it's understood at all. Nobody thinks about an oxygen sensor, not even when the check engine light comes on. Among belts, chains, wires and pumps under the hood, the battery is rather obvious. A battery's purpose is well known, and there's a warning light for it. The light that lies.
The battery light doesn't actually reflect the state of the battery at all. It indicates, to a degree, the alternator. The alternator is what charges the battery back up. It generates alternating current which is then turned into direct current. Were it simply direct current, it'd be known by the more recognizable term "generator". Feel free to skip the next paragraph, which has the exact details.
The engine typically needs somewhere between 8 to 10 volts to keep running. A fully-charged battery produces 12.6 without a load. Testing the battery is a messy affair, as it involves charging and then stress-testing, to see if it faithfully retains the power. The voltage tells nothing, as a bad battery with a high internal resistance could provide the full 12.6 when unused, but fail to deliver even the 10 volts needed when starting. Similarly, a good battery drained from leaving the lights on won't have any voltage, but once recharged, will keep on working. The alternator is powered by the engine with a pulley on the serpentine belt and should produce anywhere between 13.2 and 16 volts. The battery light is a simple voltmeter, and lights up should this voltage fall too low.
The light lies, if taken at face value, because of this. When the car's off, the alternator produces nothing, and the light goes on despite the battery's state. And when the car's running, the battery's state is hidden by the alternator's voltage. Indeed, on an older car, you could theoretically start the car, disconnect the battery, set it on the ground, and drive off with no problems as long as the car's running. (I don't suggest trying that, however. In modern cars, batteries act as voltage stabilizers for the electronics, and some cars will die while driving when the connections are loose. Most importantly, mishandling the battery connectors while the car's running can lead to injury or death.)
Got that? Now here's what I tell people, when their eyes understandably glaze over at the word "Alternator". Think of the car like a cell phone. The car is the phone, the battery is itself, and the alternator is the wall charger. In terms of complexity, it could be argued that the cell phone is more complex. But its visible parts are relatively obvious and are seen everyday. So the understanding is nigh-instantaneous.
But even a cell phone has mislabeled icons. The 50s-era antenna for signal strength. The AA battery shape despite the actual battery's shape. There is a generation of cell phone users that have never even touched, let alone used, the rotary phone whose image represents "start conversation" and "end conversation" (do you actually "hang up" a cell phone?).
But there's no alternatives. The car has a battery logo because an alternator icon would be anyone's guess. (Perhaps it should be a lightning bolt, instead). The oil icon is of an Aladdin-era lamp, which wouldn't even use the right type of oil. But little else differentiates it from water or transmission fluid. I suppose more accurate icons can be made. On some trucks, gears represent a transmission, with a monkey wrench next to it. Perhaps an almost steam-engine-esque crank for the oil that works on the crankshaft of an engine. But this presents itself with a new dilemma. In aiming for accuracy, will we defeat the icon's purpose?
The latest engine icon is a simplified outline of the engine. And I've seen people confused by it, since it's a rather obtuse shape out of context. And ironically enough, it's still not accurate. The T shape on the side represents the fan, which typically isn't connected to the engine, but instead would be an electric fan on the radiator. And the T-shape up top represents an air filter and carburetor, which was replaced by fuel injection back in the 80s and 90s.
At some level, all language is a series of icons. While patently obvious in asian scripts, even our alphabet have an iconic origin. For example, the Phoenicians' A was derived from an ox head. Its descendant's abstraction doesn't affect its utility, but it's an entirely different use. The modern reader wouldn't make the connection.
As images travel from accurate representation to an abstract unrelated, it creates inertia against newer, more accurate icons. This tradeoff between accuracy and recognizability has always existed, but a happy medium needs to be obtained before more symbols devolve into "Check engine" lights with indecipherable numeric codes.
