Manjoo is right that unlike the rest of the technology we use everyday, battery technology hasn’t evolved all that much over the past few decades. It’s constantly being refined and perfected, but it’s still largely the same. Want more battery life? Get a bigger battery.
This is simply not true. It just seems like it because batteries are a component of things we use vs. being the actual thing. The iPhone 4S is more powerful than the first laptop I owned 10 years ago. It can hold a charge for an entire day pretty much even with regular use. The laptop I had in 2001 had a battery bigger than the iPhone itself and came nowhere near powering my laptop for an entire day.
Batteries may not have shrunk much in size, but they hold far more power, and use it much more efficiently than they used to. The problem is that our demand on batteries has also increased, so there is zero net effect and it seems like things haven’t changed.