For regular battle themes, I’ll submit the only memorable song from Monster Lab (well, the DS version anyway): https://m.youtube.com/watch?v=N-ZuMaS8cdk
I very distinctly remember playing Monster Lab on the Christmas I got my DS, so it’s something I have a lot of fondness for.
For bosses I can’t not post the best song in the PC game Chrono Ark: https://m.youtube.com/watch?v=IjN1Icb-rAA