It's not the batteries that have changed, it's the circuitry. In older devices, batteries were required to power SRAM, which uses very little power (just leakag

It's not the batteries that have changed, it's the circuitry. In older devices, batteries were required to power SRAM, which uses very little power (just leakage currents). This has largely been replaced by flash memory, so if you see a battery in a modern device there's a good chance it's powering a real-time clock, which use a fair bit more power in comparison. I'm sure there's a big difference between different implementations of this -- low power design is an art that's quite easy to get wrong.