Just curious?
I know the automotive battery chargers have a desulficator and battery maintainer (trickle charge). Other than that, is there any real difference?
An alternator is a device that creates alternating current from rotational energy.
A battery charger takes mains current, converts it to DC, and supplies it to a battery in a manner that is designed specifically to charge the battery in the best way possible.
They are two very different devices used for two very different applications and are not really comparable.
The alternator in a car gets its rotational energy from a drive belt attached to the engine's crank pulley. The alternating current that it generates passes through a rectifier which converts the AC to DC. In automotive applications the voltage regulator is typically set for around 13.8 volts DC, but non-automotive alternators may generate any voltage, depending on their design (the AC power for your home comes from giant alternators, usually driven by some form of turbine, for example). In an automotive application, both the rectifier and the voltage regulator are typically built into the alternator housing and all three are sold together as an "alternator" by a parts store.
The alternator is effectively a "dumb" device. As it functions in an automotive application it simply tries to maintain a set voltage level.
So why doesn't the alternator overcharge the crap out of your battery?
Because the battery is wired in parallel with the rest of the car's electrical system and, as a result, the car's electronics can place a load on the battery. When the battery is undercharged, this load will cause the voltage level to drop, at which point the alternator will start providing more current. To borrow an explanation from another site:
Amperage or current is regulated by the state of charge of the battery. When the battery is weak, the electromotive force (voltage) is not strong enough to hold back the current from the alternator trying to recharge the battery. As the battery reaches a state of full charge, the electromotive force becomes strong enough to oppose the current flow from the alternator, the amperage output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5.
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http://www.carparts.com/classroom/charging.htm
Basically, the voltage regulator "sees" that the fully charged battery is capable of keeping the voltage at a higher level and reduces the amount of current generated by the alternator.
The two are very different things for very different roles.
ZV