Older, smaller laptops use less energy...

The "average" laptops from years ago use "roughly" the same amount of power as the modern laptop of today... The difference is that today's laptop has a much higher clock speed and is much faster than the old laptop. Mainly because the "transistors" of the modern micro processor are much smaller than the predecessors. Each transistor (and interconnects, etc.) have capacitance--Make the transistors and other features smaller, then there is less charging/discharging of capacitance.

The newest low power processors are more efficient yet--And use, on average, less power than the older laptops (and the same size battery can last several hours longer). Also, the old computers had much less memory then newer computers--Again, smaller memory transistors, less power, but cram 10x more memory in the same space (and make the memory several times faster, and the power usage goes back up again.

But if you crank up the clock speed of the low processor, run video/games/heavy processing, they can use a fair amount of power too.

The thing I have been seeing is that trying to get a 10 year old laptop or computer to run the modern OS's (Windows, Lynix, etc.)... Can barely get them to boot Windows XP SP3 or Linux Mint on 250 MBytes of memory, and run slower than heck (hardly run at all). Yet, these machines were reasonably capable back in their day.

-Bill