Chevrolet Repair: Battery, alternater, couple seconds

Question
When I got into my car yesterday, I put my key into the ignition to start the car, and at first everything was as it should be with lights and power, then after a couple seconds everything went dead. I have automatic everything, so the doors would not lock and nothing worked inside the control panel and the radio did not work. After I sat there for a while, just enough power came back to light the interior light and lock the doors, as well as give the control panel just enough light to be seen but not a lot. When I tried to start the car again it all went dead.  This morning I put water into the battery and cleaned the cables, but this did not work. I am going to take the battery to get it tested, but should that not work I am puzzled as to the cause of the problem. I was told by someone that there would be no power at all should the alternater be gone. What is your opinion on this? Thank You.

Answer
The alternator is there to recharge the battery, but the car can run several hours on just the battery, without the alternator working at all.
But with the alternator not working, the battery will be discharging, and eventually act just like yours.

They may well check and charge the battery, and tell you it is good.
Then I would suspect the alternator.

Van