I intend to go busking on keyboard soon, but I don't know how to power it. Some sites seem to recommend a car battery, but others say that that might damage it. I've also seen portable power supplies suggested, but I can't find any that are in stock. What is the best solution?
The most common way to power busking equipment is to use a deep-cycle marine battery and an inverter for the voltage and current you want to run at.
The article below also discusses almost-silent gas-powered generators, which are pricey.
If your keyboard takes batteries and doesn't eat them too quickly, then you might consider using rechargeable batteries and a battery powered amp such as the Peavey Taxi or Limo amps.