Laptop powerbank 12v to 20v and upto 5A output using 18650 batteries with USB 5v added

Hello ladies and gentlemen. 

Im looking into buying a laptop powerbank charger for my Lenovo X1 carbon that charges at 20v 4.5A 90w fast charge with upto 80% charge in 1hr. But it will also charge at 65w and maybe 45w I've read. But this will not give me the full power of the processors and gpu etc. Unless I charge at 90w 4.53A 

there are are some powerbank that are around £100-170 for sale but these don't give full 4.5A. Mainly around 2-3.5A so will maybe or maybe not charge she give me full power of the laptop  

so I'm thinking about making me own using 18650 batteries. Good Samsung or LG 2500maH plus cells. Prob around 3000mah. 
Im thinking I could either use a buck down or step up and use the batteries on series from 3S to 8S and then 3-4P to give me around 10000mah. I'm looking for the best efficient output so I'm not sure whether to use higher input or lower input to give me 20v. 

Or or maybe I could go the inveter route using a 12-24v 150w inverter?? Efficiency is the main thing here. What is the best option do you think. Should I use 12v or 24v for max effecient conversion. 

Ive searched the instructables for such devices but cannot seem to find anything like this. Or would I be better to buy one??? I would want to add USB and USB c also. Defo USB 2.0. 

Could you you please help me choose and find the answers please? 
I fancy the DIY route because I'm looking into solar and battery power storage and also boost my range wifi range through either ptp or directional attenna. These projects will come after the laptop powerbank. 

Any my help would be appreciated a lot. 

Kind regards. 
Scott. 

I actually built something very similar to what you're describing here for my own laptop a little while ago, I can give you a few suggestions for your build you own idea. For the basic design, I would go with a 4S x 4P battery pack followed by a boost converter. That'd give you a voltage range (charged to dead) of 14V-16.8V and a capacity of 10,000mAH. Little tip on batteries, if they're rated above 2,600mAH, they're most likely fake. Also, it's usually cheaper to buy something like a USB power bank and steal the batteries from that than it is to buy them separately. I would suggest this ( https://www.amazon.com/Lumsing-10400mAh-External-S... ) power bank as I have bought and tested it personally and can verify that it does in fact have 4 2,600mAH 18650s inside. For the boost converter I would suggest at least a 150W one, though it will get quite warm running 90W continuously. Something like this converter would be good. ( https://www.amazon.com/DZS-Elec-Converter-12V-32V-... ) Also keep in mind that you will need a 4S battery protection circuit, something like this ( https://www.amazon.com/15A-Lithium-Battery-Protect... ) and a 4S li-ion or lipo balance charger, something like this ( https://www.amazon.com/EV-PEAK-50Watts-Battery-Bal... ) Both of those, while inconvenient, are absolutely essential for a safe system. Finally, for the USB output, a 5V buck converter works perfect. I used this circuit ( https://www.amazon.com/Ailavi-Converter-6V-24V-Out... ) which has a 3A output, plenty for one fast charge port or two medium speed ports, and I can verify that it does charge devices quite speedily. Just connect it in parallel with the boost converter. Also, seems obvious, but I usually miss the obvious, make sure to put a switch between the protection board's output and the input of the converters, as they draw some power even when nothing is plugged in. I hope this helps a bit and would love to see your finished design!

~Josh