It can even connect to a PC and give you a full "Data-sheet" graph of the discharge and total capacity.
Note that this is my first Arduino project (I am not counting my "blink LED").
Step 1: This is what you can get at the end...(just to get you interested)
Step 2: Lets start at the begining - Arduino
Step 3: Bread board Arduino
most of the information can be found in the Arduino web page :
They realy have everything you need .
It took me about a week to get it up and running (bootloader / building an ISP cable and an RS232 cable ...) - you can read all about this in the site above .
Step 4: FET with 2.2Ohm load
I connected two A/D pins from the Arduino to the resistor poles and subtracted the values to get the exact volatge drop on the resistor .
Now I samples them every second and acumulated the current (I=DeltaV/R).
I also added a buzzer to indicate when charging was over and stoped the discharge .