How to change the battery in a 2003 Honda Accord
This technique is pretty general and applies to the 2004, 2005, 2006, 2007 Honda Accords also. In fact, it probably applies to most cars out there. It's quite simple.
A multi-point inspection revealed that our battery was nearing the end of its life. It was about 5 years old, so I think that's normal. I was quoted $107 over the phone and, not being fancy enough to have an internet phone, was almost certain I could find a better deal another day. I looked it up later and found out that even Advance Auto Parts sold the Accord battery for about $100. I should have had the dealer change it.
I drove down to the Advance Auto Parts, bought the battery, and opened the hood of the car. There's a bracket holding the battery in place. Loosen one of the nuts and pull the bracket out. You don't have to completely unscrew anything.
After that, loosen the bolts on the battery terminals. I started with the red terminal. Loosen both enough to pull the cables off of the terminals. After that, pull up on the plastic casing that surrounds the battery. You can now pull the battery out and place the new one in.
Note the comments below: start with the black terminal first.
Put the plastic casing back on, attach and tighten the bolts on the terminals, and put the bracket back in and tighten it enough so that the battery is secure.
Start the car, press the On button on the stereo. You should see the word "Code" appear on the stereo display. Make sure you have your anti-theft code. It's written on a small card (business card size) and probably came with your owner's manual and documentation. Enter the code using the preset radio buttons (1-6). You should hear a beep and after that you can reprogram the radio.