Ensoniq SQ1 Plus Battery Replacement 

I haven't had that issue, however I found the following information online: Method 1 - To perform a hard reset on an Ensoniq SQ-1, you can try the following steps: Press EDIT SEQUENCES / PRESETS Press and hold SYSTEM (Bank 9) Press Screen (9), then release both buttons The display should say RE-INITIALIZE ALL RAM? Press YES This will erase all RAM and reset all internal programs with ROM sounds. Method 2 - Turn the unit off and then on slowly (at about 2 second intervals) seven times. The eighth time you turn it on, the unit will automatically reinitialize itself and should show the wake-up screen. I hope this helps. Best of luck.

It's been so long ago, I couldn't locate the exact one. This one should work though: amzn.to/48wltaY

I have not come across that error message. You may try to google it. Sorry I couldn't be of more help.

Yes the keyboard will still play but it will not retain internal memory after you turn it off

I'm not sure.. fortunately I haven't run into that problem yet. Good luck!

Okay thx anyway..