It works.
As a battery it certainly works, but thought it does boast a longer battery life, it really doesn't have one.

When my original battery started to last shorter hours, I ordered this as a replacement, but saw no improvement.

If you need a replacement for, say like a long plane ride with no way to charge, this might be an okay way to go about extending your play-time though.

Only passable as a cheap replacement...
My original Nintendo DS Lite battery was beginning to wear down after much use and recharging, so I decided to try this one as a replacement--the official Nintendo DS Lite battery is 1000mAH and this one boasts an "extended life" of 1200mAH... however, after much use (and switching back and forth between this battery and my old one to make sure I wasn't imagining things) I was getting half as much battery life out of this battery than my used, official Nintendo DS Lite battery.

If your current battery is just plain dead or you're looking for a cheap additional battery for your DS Lite, this one will probably suffice, but I'd steer clear of this one as a battery for everyday use.