Ok, so many users will feel these are substantial enough for most usage scenarios, but it really does depend. (mobilegeeks.com)
That said, you should still be able to get a day's worth of usage out of the battery in most usage scenarios. (androidcentral.com)
Maybe someday that will be replaced, or augmented, with carbon fiber — it's still too expensive for most usages now, but prices could fall significantly. (treehugger.com)