[OMGWTFBBQ]

I say "odd" in that I know that is likely not something that many people would want...

Is it possible to do the following?
Have the power cord for the laptop plugged in, but have the laptop run off of the battery until the battery is dead. Then it switches over at the last minute to the power and runs off of that and charges the battery.
Then once the battery is full again, it goes off of that and doesn't draw on the power.

I know this seems daft since one might disconnect from the power cord at any minute and then want to travel and they could feasibly have a very nearly dead battery were one to follow this concept out.

And also, I mean for it to be fully automatic, no human intervention beyond perhaps flipping a switch via software or hardware. External software options would be fine as well.

The reason I ask is that in the line of work that I am in, there is a demand for large clusters of computers to do computation - along the lines of the Big Mac.
In those situations, it isn't always the case where you need the processor to be the fastest thing available (again, say the G5 in the Big Macs), but you just need a lot of them.
It is clear that many computers running will draw a lot of power - so one way around this is to have battery powered computers in the cluster - that way they aren't always drawing on the power, but only once the battery is run down.

If we have a hurricane here and the power is knocked out, a generator can keep it all going for us. But if we have a cluster of computers going, it is going to kill that generator. But if they are cycling through their own batteries, that can help us a lot.

I would assume that there are hardware ways around this (UPS variants), but I thought I would see if a random idea - this one - had any backing to it. Were it feasible, I could then price out other options to see if this option is as cost ineffective as I would immediately assume that it would be.

[OMGWTFBBQ]

Of course the other benefit of clustering laptops is that they take up much less space than even a rackmount system.
Not to mention they are far quieter.

It is not a cheap method, but if you are trying to save power, space, and noise - as well as have an easier time cooling the system, it is an interesting way to go.

The downside is that you have a screen on every single unit, which is terribly wasteful since you wouldn't really ever need that screen (one could make arguments that the screen is a good thing for emergency maintenance).

Any ideas would be much appreciated.