Sega CD Model 1 VS Model 2 which is better?

The CMOS replacement battery is ML2016, purchase one that has solder tabs pre installed. Also 2 things I failed to mention is that early model 1 systems have a BIOS chip that is socketed! This means you can buy or have someone create a custom BIOS that will allow you to play any region game. Theres videos on YouTube going over this.

The other is that Model 1 systems required the use of a " an audio mixing cable" this is just a regular 3 foot auxiliary cable that plugs into the Sega Genesis Model 1's audio out jack in the front (set the volume slider on the Genesis to 8 as per the SCD user guide). The other end plugs into the "Mixing" jack on the back of the model 1 and model 2 SCD console. This allows the SCD to mix the audio from the Genesis with the audio from the SCD together. If you dont use the mixing cable you'll still get the audio from the Genesis but it'll play in mono only while the SCD audio will play in stereo. Model 2 systems don't have a headphone jack a will play audio in stereo regardless of how you have the audio hooked up, assuming you're using stereo out cables to begin with.