I noticed that my 04 Accord was cranking a little slower than usual and with the winter months upon us, I wanted to replace the battery before I got stuck. I bought the Accord used and didn't have the radio code. So I used jumper cables from my wifes van to the battery cable lugs on my Accord. After carefully removing the battery cables maintaining the connection to the jumper cables I was able R&R the battery, reconnect and not loose any radio data.

I believe that this can also be done with a small 9v transister battery but I didn't want to take the chance.

I've seen these at a local autozone. Not sure it they actually work tho.

Or you could just go here (https://radio-navicode.honda.com/) and enter your vehicle info and BAM! You've got your code.

Oh yea I forgot to say when I called my local dealer they said after I install the battery they will remove my radio and get the serial number off the back of it and get the code. The dealer I bought the car from said that I could call them and they would walk me through getting the codes. This reminds me of a Volvo I had that I needed to go to the dealer to reset the maintenance light, B.S., IMO.

Yea, the Autozone tool is a 9v battery that has an adapter to plug into your accessary outlet. I was too cheap to spend the $5.