Laptop requirements?

[curious aardvark]

it's actually cheaper to build a new base unit. Plus that way you get much faster processor - and don't believe emu. If you use openscad - you want a decent processor.
Also some of the slicing engines benefit from a decent processor as well.
On top of that some of the cad packages need a decent graphics chipset.
And if you're got an sd slot on your 3d printer, then you've probably also got a control panel. So preheating can be done without an attached computer.
As can most maintenance tasks.

My advice for a cheap unit for 3d printing.

processor:AMD APU Athlon 5350 Quad Core Processor (Socket AM1, 2.05GHz, 2MB, 25W, AMD Radeon 3
motherboard:MSI AM1I AMD Mini ITX Motherboard
Ram: any 2gb 1600 ddr3 dimm
hardrive: cheapest 64gb ssd (solid state drive) you can find.
At the very least get a hybrid drive. That way the 8gb used most runs from a ssd anyway.
You don't need a dvd drive, if you do buy an external usb powered one. Same price as internal and much more useful.

I've built a few of these in the last month. For general desktop use and with larger ssds in.
I'm also using one myself, but with the cheaper 1ghz quad core in. That also does a decent job. At some point I'll drop a 5350 cpu in, as openscad would definitely benefit from the extra oomph.

And that's it.
Either drop it into an old case, or make or buy a mini itx case. I built a 17x20 cm 3 sided, wooden box, drilled 4 holes for screw lugs and took an on off switch from an old base unit.
add an old monitor, mouse and keyboard and you're good to go for less than a reasonable second hand base unit

Small fast solid state drives are much better than huge traditional mechanical drives. You won't be storing huge amounts of data and the ssd makes windows run 10x faster than standard drives. Supposed to be more reliable as well. But given the manufacturers claim 2-300 years mean time before failure, nobody actually know yet whether they last longer than mechanical drives or not :-)

Laptops are prone to overheating and cutting out. Second hand laptops doubly so. Having been in the industry for 20 odd years, I can confidently state that nobody ever sells or passes on a fully working laptop. Even if it just needs a new battery - there will be something wrong with it.

My opinion on dell equipment is usually unprintable - throw it away and make your own :-)

Laptop wise - go for one with amd a-series Apu - the a8's are faster than i7's - and yes I've benchmarked both.
Amd chips are faster and cheaper than intel chips and the onboard graphics is much better than the intel hd chipset.
I haven't used intel processors since amd first released it's 486 chips, going back nearly 20 years I reckon.
Amd chips are just better - and cheaper :-) And yes i do a lot of benchmarking.
We're talking thousands of machines. Built and fixed over 20 years as a professional.