I plugged in my Kawai K1 tonight after a few weeks or months of lack of use (i really can't remember when I last used it).
The display lights up, but remains on the "*Kawai K1* synthesizer" message. A couple of times I've managed to get it past that, but editing is erratic and much of the time the buttons don't work. My patches don't seem to be present any longer. On one occasion it went to a modulated sound that continued without any key being pressed.
I'm inclined to suspect the battery, but I thought I'd ask here to see if the behaviour is consistent with that. There's no low battery message, so I wonder if it could be something else. I've powered it off for now in case it's a power supply problem or something.
I don't know the history of this keyboard, but it seems reasonable to suppose the battery has never been replaced. I bought it for £10.50 three or four years ago with some broken keys and bits rattling around inside. I was told it had had a DX21 (or maybe DX27) dropped on it. I got the bits out and replaced the broken keys. It's always worked well and I've edited it extensively with no problems before tonight, but I don't use it very often.
If it's likely to be the battery I'll take it to a tech, but if it's something serious I'll probably sell it for parts as I got it cheap and it hasn't been a major instrument for me. (I wish I'd sampled it, though.)