After seeing confusion of diagnosing big "Ks" electrical woes - I figured I'ld make an attempt to eliminate some of the mystery behind your electrical/charging system.
#1) get yourself a volt/ohm meter - they're cheap & SUPER simple to use. You can get them at Home Depot, Radio Shack & tons of hardware places. You can get them from under $10 up to $5-600, but for simple testing - cheap is good (see below)
#2) attatch to your battery when car is off - you should get a reading of 11.5 - 13.0 volts. (the higher the better - means your battery is not terminally ill -sorry about pun)
#3) Now start car and check readings - it should read at least 12.1 up to 14.8 volts - anything below that, your alternator is not charging anything over it means the alternator is overcharging battery. Also while car is running (for all of you with mega electrical toys added) start turning on each one - one at a time and see how much affect each gadget draws and affects charging system. If you see volts dropping big time... you might want to check the gadget and/or if gadget is ok, you might consider going to a larger alternator.
See pics below in sequential order.