Umm..... I think this fine for begginners corner as it is the simplest type mod known to man and a good place to start.
Samus-Fan, to answer your question, there is something that you use in order to control the amount of Amps, it is called a limiting resistor, and is put in series with the LED in order to limit the amount of current flowing.(voltage is constant value for LEDs so it either has enough to be on or not on)
The first issue with your idea is that if you hook LEDs right to the battery voltage they will be on as long as the battery is in, unless you use a switch to shut them off.
the next issue with battery voltage is that while is stays pretty much the same voltage for most of the battery life, eventually the battery voltage will drop, which will cause your LEDs to dim out as the battery dies.
So both of the above issues can be fixed by finding a powersource on the DS that switches on and off with the DS, as well as remains the same voltage(regulated)throughout the battery life.
So this is where you would want to look around the DS section, as well as google, and see if such a voltage source exists.
Once you find the voltage source you can begin to calculate what is needed to run LEDs from it.
you need to know the voltage of your source
you need to know the "forward voltage" of your LED
You need to know the forward current your LED runs at.
The LED information is found from the associated specifications sheet or from the seller.
Once you have the information you can plug it into
this handy LED calculator, and it will tell you what resistor value you need in order to limit your LEDs correctly.
If you are using a bunch of LEDs it doesnt hurt to try the
LED array calculator
