I've got one, and seriously, I haven't noticed it to be dim outside. It's brighter than the 3DS, if you have ever used one of those outside.
As for charging, I don't have any figures, but if you have a USB power bank, you'll still be able to keep on going, and anyway, with games like Zelda, you're still going to get like 3 hours of battery life. I can't imagine anyone sitting outside for more than 3 hours xD.