Portland is an incredibly bike theft prone city. It may be #2 behind NYC despite having fewer actual bikes than many other cities that rank lower. Bikes are one thing, bike accessories are another. I no longer bother to take my lights off my bike. I've had two bikes stolen in 10 years. No lights stolen ever. Not scientific and very small sample size but there you are. That said, my lights are MagicShines, they attach with O-rings. And they look for all the world like the ridiculously cheap lights you can find on Amazon for $20. For fancier battery lights they will ALWAYS have some kind of bayonet mount that allows them to be easily removed. The battery packs as well. Those are the lights that will be taken (maybe) if left on the bike, but since they are so easy to remove, I always do that, or did when I had expensive lights. I am not that certain that dynamo hubs produce A/C. I would doubt it. They all produce about 3W at 6V and the light electronics are designed to work with that. The issue with using batteries to power dynamo lights, besides the voltage mismatch, is the hook-ups which I have never actually seen never having owned a dynamo light but which I imagine are incompatible with the connectors often proprietary, from the various makes of battery packs in use. No matter how inexpensive a light might be modifying its cables becomes more work than simply buying a cheap battery light and replacing it if stolen. That's what I would do. FWIW.