Na na na na na na na na Batman!
That's right, it's a wristband battery and it comes with a connector that fits the 3DS. Specifically, it's designated as a DSi/DSi XL adapter, but it will fit in the 3DS perfectly since they use the same connector.
Coming in at $35, it's more expensive than the 3DS specific battery replacement Nyko is offering, but it will fit more gadgets, and leave your 3DS looking like it did the day you got it, if those things are important to you. The battery is rated at 1800 mAh, whereas the 3DS' battery is rated at 1300 mAh, so it's conceivable that this will at least double your play time with the 3DS while in use. If/when the battery life of the 3DS starts to bother me, then this is definitely a product I will consider buying. It has an adapter for iPhone and mini-USB among others, so depending on what you own, you could get a ton of use out of this.
If you guys were considering the Nyko battery, is this a more appealing option? I'd love to hear why or why not in the comments.
You can buy it right here.