Anyone tried this one? I bought the Ravpower initially for my beach amp (Crate and KC-110). They work great and the charge lasts forever. In this video, the guy claims he has played his 88-key Casio for 5 hours and he also ran a tablet out of the same battery.

This battery comes with a plethora of connectors. I have used it to power my KC-110, Crate, and several of my Ham radio transceivers. I recommended this to another beach musician (guitar player/singer) and he said it is the greatest thing since sliced bread - he powers his KC-110's with it. Anyway, another possibility as I see a lot of the Yammies are running on 12V power.