Here’s an app note from Maxim – Technology Changes: From a portable power point of view
Portable power presents a range of design challenges. While major changes such as new battery technologies make headlines, the minor, almost negligible shifts are arguably more fascinating. The effects of these shifts is often non-linear µ a small change triggers a big change! Major shifts like this happen when battery technologies, dropping system voltages, new RF and display components, and, of course, power conversion advances, all interact.
the link in the post seems to be broken, here’s a direct link to the PDF which works ATM:
http://pdfserv.maximintegrated.com/en/an/AN1930.pdf