I need help finding a good lighting setup for my flagpole.?

I have a flagpole that is quite a ways away from the nearest electrical source. I am a real stickler when it comes to keeping the flag lit up at night, so it's important to me that I get a great setup. I know there are all kinds of wired options, but that would involve trenching up half of the yard and rewiring stuff in the house. Not much fun. Solar sounds great, until it's dead by midnight. (We have trees in the area, so solar isn't always a good way to go). What else is there? Do they make battery packs for lights? Any input would be greatly appreciated!

Thanks!