And drain your battery for no reason.

Do you have any proof of that? "Free" memory uses as much energy as "used" memory, there is no distinction in SD|DDR-RAM. And if the OS is smart, it only has to keep a simple index of memory pages still relevant. I'd argue that this has a measurable battery-hit.

You're only accounting for the RAM power. Accessing the SSD costs power, too.

Then I think I'd rather Windows prefetched my programs while I'm plugged in so it doesn't have to do so when I'm on battery.

> You're only accounting for the RAM power. Accessing the SSD costs power, too.

A typical modern SSD reads at 500 MiB/s, consumes 3 watts when reading, and 0.3 watts when idle.

A stick of DDR3 RAM consumes about 3 watts, just sitting idle.

The power consumption from prefetching is minor compared to that of the RAM.

Reading from the SSD to laod it into RAM does drain battery. No idea if it is enough to matter though.