Why would a car with a fully charged battery have dim lights and be unable to start?

Answer 1

If you see any white, ashy deposit around one or both battery posts then battery terminal corrosion is your problem! Any corrosion acts like a big resistor, and prevents voltage from getting through:

Battery Terminal Corrosion - How to Clean a Car Battery Terminalhttp://www.howtocleanstuff.net/auto/mechanical/how-to-clean-car-battery-terminals/ How to Jump Start a Car(Good battery info near the end)

http://www.carbuyingtips.com/jumpstart.htm

How to Install a New Car Battery | ExpertVillage videos(The video shows a battery terminal cleaner brush)

http://www.expertvillage.com/video/16396_car-battery-two.htm

Finish by making sure the connection to the terminal is tight.

It sound like you are sure your battery is good. If you have a load tester then hook it up and eliminate the battery as the problem. Dim lights and a no crank condition indicates a supply problem to the relay box under the hood. The cable running from the positive battery post to the relay box may be partially broken or have a bad connection. A voltmeter may read 12 or more vots suppling the relay box until the key is turned on. Then the volts will quickly drop and stay low until the key is switched off. This is because the faulty cable or connections can't keep up with the power demands of the lights or starter. You can also use one cable in a set of jumper cables to connect the + side of the battery to the relay box power supply post(the place where the power cable connects to the box). This should teporarily supply enough power and will indicate whether or not the cable is faulty. Have fun! Chris

Digital volt meters will put a load on any voltage source you measure. Turning on the headlights will show a drop in voltage, turning them off will show the voltage upswing. The amp hour rating is what allows the voltage to remain high for a long period of time. Sounds like something is shorted, drawing down the voltage, not allowing enough voltage to reach the starter. Check Battery cables first if good and if you hear clicking coming from the starter solenoid check the starter, If no sound is coming from starter check the fuse, or fusable link, and check the ignition switch.

it could be that your ground cable (neg.) might not have a good connection on your frame

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I personally would make sure the battery is fully charged and take the battery and have it checked most places like Walmart and autozone will do this for free. Check the battery if possible making sure it is full of water up to the eyelets if not fill it with distilled water up to the eyelets and recharge. Next guess would be the clicking sound is the starter solenoid engaging However it sounds like the starter may be dragging and or shorted. When you connect the battery to the cables with everything off if it makes a rather large spark I would suggest a short in the starter or somewhere. EzForJesus

Based on my experience, I believe your battery is not charged, as I have experienced the same symptom.

I believe the manufactures have changed the way the newer batteries are constructed. The end result of this is that you can measure about 12 volts across the battery with no load. The only way you can verify the proper battery voltage is to put a load on it, such as turning on your headlights. My guess is you will then measure a voltage value around 10 volts - or to low to start your car.

Regards