As a smartphone or tablet extensions, smart glasses could be fairly useful. As primarily stand-alone devices though, I have a hard time imagining myself using a device mostly with voice commands and head gestures. With eye-tracking navigation, they would become a fair bit more practical as stand-alone but it would also eat batteries like nobody's business.
I have no doubt smart glasses are here to stay but we are still 5+ years away from this achieving truly mainstream functionality and pricing.
So does it have an improved battery [capacity], or just improved battery life?
Most likely a slightly bigger battery, a more power-efficient SoC re-spin, an updated VRM to go with that and a handful of software tweaks. It has been nearly two years since the original Glasses prototypes so hardware is bound to change a little even if only to keep up with old part models getting superseded by slightly improved drop-in successors before the old parts get discontinued.
Tech like this is, in my opinion, exactly where technology is heading. Once augmented reality really gets going these are going to difficult to live without. Obviously the first few generations are going to be a bit rough and I'm not convinced that voice commands are the best way to go. However, give it another ~10 years and these will change the world. It took.
The first public mobile phone network with widespread use was in the 1940s and it wasn't until the 70s that truly mobile phones (i.e. handheld) phones came out. Even then it wasn't until the 1990s that mobile phones really took off. Given that technological progress keeps accelerating, I'd think that we have 5-10 years until they are actually really useful and 10-15 years before they become mainstream.
Given that technological progress keeps accelerating
Accelerating? Mobile SoCs still have a long way to go to catch up with traditional desktops in terms of raw processing power and the processing power growth on SoCs is already starting to taper off, the amount of RAM in mainstream devices has been stagnating in the 1-2GB range for the past two years, mainstream internal storage has been stuck at 16GB and I'm sure there are a few other things that are stuck in the past too. High-end devices from 2014 are for the most part the same as their 2013 counterpart except for updated parts.
While things on mobile are still moving forward faster than desktop (mostly because they still have a huge gap to close), mobile computing is not advancing anywhere near as fast as it did 2-5 years ago.
The only thing on mobile that is growing ridiculously fast is pixel densities beyond human sight which seem like completely unnecessary waste of processing and battery power to me.