Does swabbing work? I can imagine that the "batteries" (ie bomb) would be prepared, sealed and cleaned by one person, and then inserted into the laptop by another person so there's no contamination.
It's hard to remove all trace, but yes, in theory you could avoid it by being really careful. Then again, if you work in a "bomb factory," there's trace everywhere, so it may be quite difficult.
Also, the "turn on your device" thing they sometimes do offers some mitigation against this. Obviously, you can think of ways that may defeat this too, but to defeat all of the security, accurately, in one small package that doesn't look sketchy, is not easy. Fortunately, most terrorists are not the brightest people in the world.
That would already cut the amount of explosives in half. Modern laptop batteries are not exactly huge to start with. So it is much less likely to do big damage to the airplane. Add to that, it is not trivial to make a battery half the size which still has enough voltage to power the laptop - you would need cells half the size for that. And all bombings of airplanes have been done with bombs in the cargo bay.
Also, the "turn on your device" thing they sometimes do offers some mitigation against this. Obviously, you can think of ways that may defeat this too, but to defeat all of the security, accurately, in one small package that doesn't look sketchy, is not easy. Fortunately, most terrorists are not the brightest people in the world.