Thank you for your answers. As for my WK 4 I won´t give up hope for now – at least I have found a suitable battery …

Regarding the left hand issue I´ve been practising Teds' suggestion for about ten years, while using my KORG i30 on stage. Many styles were okay then, some sounds as well. But for an acceptable piano sound I used a yamaha-module, and some more modules for realistic drum sounds, bass etc. So I had to transport and assemble quite some racks, which took time and energy. That was the price for an almost perfect sound!

I am now 76 years and glad to have all that stuff in one keyboard (Ketron Audya 5). Of course not everything is really perfect now, but largely acceptable, especially in relation to my age and my limited physical abilities. You know, as get older you become a bit more comfortable (and always a little lazier).