Rockhen, what about running it off a car battery? I know they're heavy and it's another thing to lug, but with a mains converter (or whatever you call them) you should be able to get it to talk to your keys and power them up. My partner once made me an external battery-pack out of some rechargeable nickel cadmium batteries (now surpassed by better types) which was smaller and more portable than a car battery, though less powerful. I think he used a mains lead that he got from a car shop or a boat-accessories supplier (it was a long time ago) but it worked.

If people give you a hard time about being "electric" it probably means they're afraid of getting blasted out by amplification. Point out to them politely that you're only going to sing ACOUSTICALLY over the sound coming out of the keyboard's built-in speakers, which in fact can be turned down to a quiet level. They often don't realise this and assume you're going to start hauling out mics & amps & speakers.

This was many years ago, but: I once caught an unbelievably hard time from one of the regulars (not the organiser) in a club where we were the booked guests, for daring to bring in an electronic piano. I hadn't seen anyone so rude and insulting in a long time, much less been the target of it. But after the gig - in which I had sung acoustically over the traditional organ & harmonium voices plus the piano and the harpsichord - he was apologetic and embarrassed.

Play your piano whenever and wherever you can, and enjoy it. The best way to eradicate prejudices is to show, not tell. And the best thing to do with all that music locked up in your piano is to let it free!