The Kawai & Teisco Analog Synths Group

Hello all, I searched the archives so apologies if these subjects have been definitively responded to.

Can I use this synth without a battery (in other words, if I desolder the internal original NiCAD battery, will the synth work as normal, save for the inability to save presets?)

My SX-240, which I just received, is in near-mint condition cosmetically; however when I turn it on, four consecutive notes in the lower half of the keyboard are constantly droning. Does this mean I have circuit board damage from a leaking battery, or just that said battery is dead? 

Where can I find a replacement LI-ION battery as opposed to a NiCAD (I found links in previous posts to NiCAD batteries but I don't want to deal with a hazardous battery once again in 2024!)

Finally, how many of these synths were produced? I have read estimates including 1000 and 3000 total. Has anyone got the definitive number or something close?

Thanks for your patience and time!

- JB