I have a first gen DS, and my battery is fine. Mine's just a bit battered and covered in stickers ^_^
I've discussed this so many times lol, so I'm going to be lazy and copy and paste from another forum I replied to.
I like the camera because I don't have a camera phone, I do have a camera but it's too big to carry around unless I have a specific reason too. So for when I'm bored during my break at Uni it would be fun to have to annoy my friends with lol
I don't mind not having a GBA slot, because I don't play that many GBA games, plus I have a GBA and will be keeping my DS. Also when they made the GBA they didn't make it compatible with a few GB games, the DS isn't compatible with any GB games either and people complained about that. So having the new DSi not be compatible with GBA isn't new, nor a particularly big deal really.
I really like the idea of being able to download games and hopefully the Wifi will be better because my DS won't let me connect ;_;
I think it's a little annoying that it can't hold MP3s, but I don't mind converting things really, I love my Zen Mirco, but it I only have to carry a DSi in my bag for Uni and everyday, rather than my DS, MP3 player, headphones, purse, umbrella, books, pens, drink, camera etc then that's great.
I can see what people are saying about the DSi not being aimed at 'real' gamers, and people who want a fashion accesory are more likely to buy it. But I don't see that as a problem, it's good for Nintendo. I'll be buying it for the reasons I said above. I'm just glad they havn't decided to make a totally new software format that would mean new games.