Hello Tom,

If the battery has died, so has the internal memory. The ESQ-1 came with a cartridge that included the original bank of sounds. If you do not have this cartridge, you can probably find a download by searching for ENSONIQ ESQ-1 Factory Sounds.

I did this and came up with several possibilities. Here are just two:
I know if you get in touch with Syntaur they will have these sounds.
I don't know anything about this site, but it has some interesting things. Although I would be hesitant to try some of these "hacker tricks" as it could render instrument useless.

Good luck,