you are not going to grab both ends at the same time or put them in your mouth. it wont blow or f*uck anything. you dont need to know what you are doing, JUST UNPLUG THE CABLES and thats it if the car still running the alternator is fine.
Electronics DO NOT LIKE the voltage variations that are created by the alternator. Modern control systems need constant steady voltage in order to work properly. The battery is used to keep input voltage constant so that the regulation circuits on the control units don't overheat and burn out. This concept applies to ALL electronics, not just what's in our cars. Ever heard of a brown out? They eat computer power supplys and TVs on a regular basis.
The alternator creates alternating current waveform (hence the name). That means that the voltage waveform produced by the alternator changes polarity (+ - + - + -). If it were left alone like that the alternator would only be good for light bulbs. But electronics can't run on alternating current. It has to be converted to a DC current waveform by a set of diodes (known as a rectifier) in order to be used by the car. Problem is you still have fluctuations in the waveform as the alternator spins due to the way the electricity is being produced. The waveform bounces from ~14V to 0V dozens of times a second. The faster it spins the less time between fluctuations but they're still there. These changes in voltage are what causes the trouble. From that point this goes way deeper than I can explain without writing a book about the relation of voltage to amps and how all that is affected by the type of waveform being produced. But, this is where the battery comes in. The battery provides voltage between those fluctuations in order to keep a constant voltage going to the control modules of the car. Think of it like a capacitor for a big sound system. It in essence, soaks up, or "filters" out those small changes in the current.
You can remove the positive cable from the battery while the engine is running, but it's not a good idea, nor is it a valid test. So the engine might stay running, but you don't know how many amps the alt is producing by doing that. Amps are just as important as voltage. Most parts stores will do charging system tests for free. You're much better off taking the car to one of them, than playing around with the battery while the engine is running and risk killing one or all of the control units in the car.
I still say battery, although there is a possibility the alternator has a bad diode, or there is some other type of draw (sound system equipment not turning off as it should?) that is draining the battery as the car sits. But, I tend to think more along the lines that the battery is just going bad and is losing it's charge on its own.
Removing the negative cable from the battery at night and reconnecting it the next morning should rule out a draw if the battery light still comes on once the engine is started.
Or you can just have it tested.
