As far as battery life is concerned. As long as you don't actually use the 3D, which quite honestly, only gives me a headache near instantly. It's quite a lot longer. I own both a DSi and a 3DS which I bought recently with my last pay. I don't regret it. For one, I could move over my Celebi, the green little legendary thing... Secondly, I now enjoy games such as Zelda and Starfox 64 (Loved that game on the N64). Granted, those games I've both played several times over before, but man.. the nostalgia is amazing. Didn't get the XL version though, I got this.. Zelda Anniversary edition. It's black and golden.
But on topic. Is it worth it if you only play Pokemon and you don't intend to get into any other good 3DS games? Probably not to be honest. I bought a 3DS because plenty of the titles appealed to me, and I've had no regret as of yet. But I wouldn't have done it if say, only pokemon titles were my interest.
Edit: I'd also like to add that, while it's possible there might be a pokemon game with 3D eventually, that won't be anytime soon and by then, you'd have a new version of the DS possibly. So again, unless you can look into other 3DS titles and go "That's pretty cool." you shouldn't get it for pokemon. Not yet at least. Black and White 2 won't be 3DS only as far as I know, but will use the 3DS somehow, I doubt it'll be largely game changing though.