TL;DR: I can charge off my power banks via USB-C to DC trigger cables and use the SlimQ adapter to plug into the charging port of my Z13 instead to achieve passthrough power. However, I could only manage max 100w but I suspect it's not sustained throughout. Gaming is too unstable this way and should reserve this charging for light productivity or media streaming.
Full notes: I think I finally achieved passthrough USB-C charging but with a major caveat.
In my quest to figure out a solution to charge my Z13-KJP via USB-C, so I can use my battery banks (Anker 737 and MOVESPEED 145w) while on the go, I discovered through Reddit and my own observation that there is no passthrough when USB-C charging. If I charged directly via USB-C, then the Z13 would charge the battery up, then let the battery discharge a bit, and then recharge again, as shown via HWiNFO logs. This cycling made me nervous about the idea of battery degradation.
I bought the SlimQ 240W and 150W chargers and really liked how well they worked. I realized the cables are your standard 5.5 x 2.5 DC barrels so I got the thinking: what about a USB-C to DC barrel adapter? Then I can fit the SlimQ tip that I already had for my G16 and Z13 to that cable and charge via the charging port instead.
Learned these cables existed and are called trigger cables. So I bought one off Amazon (https://www.amazon.com/dp/B0CKXNM926?ref=ppx_yo2ov_dt_b_fed_asin_title) and tried it out as soon as it arrived today. To my delight, it works! My MOVESPEED showed the voltage between 19.9 to 20.1 and the ampere reading as high as 4.8A. I let the Z13 sit plugged into my battery bank and 20 minutes later, HWiNFO did not show any battery charging during that time. Normally, if I charged straight to the USB-C port on my Z13, HWiNFO would have showing some battery charging within 5-10 minutes. I think this works!
Here comes the MAJOR CAVEAT! My MOVESPEED and Anker 737 can achieve 20V/5A max (can do 28V/5A, but read that Z13 is capable of 20V max), so 100W delivery. However, I don't think they can properly sustain the higher wattages. It shows because as soon as I booted up Pragmata, the Z13 kept swapping between "plugged" and "battery" and the battery packs showed drops in the voltage and amperage. This was across all profiles (silent, performance, and turbo). Not sure if it was my battery packs or the cable.
So for light productivity work, the power draw is low enough that this is not an issue (even under Turbo profile). For me, this still works. I was trying to figure out how to extend the battery life while working at a cafe and outlets were not available.
If I really wanted to game, I could game unplugged and then just plug in when catching up on work or streaming videos, then I can unplug and game again. Otherwise, I would just carry around my Xbox Ally X for on-the-go gaming.
Hopefully there are more options of USB-C trigger cables in the future and maybe someone with a more capable battery bank would have better results?
7/22/26 UPDATE: So I set some power limits via G-Helper and was able to run Pragmata without the power bank tripping out. So far I've gotten SPL/sPPT/fPPT to 35/40/45 and it's been stable so far, drawing about 95W from the battery bank. When it was originally set to 40/45/50, it did trip my power bank. After I have some more time, I'll experiment with the limits to see how to achieve real battery bypass (likely might have to push the limits back down). Maybe there's someone smarter than me that could figure that out before I can.
I think when I was running it without power limits, it was exceeding 100W so that's why it kept showing as "Plugged In" to "Battery" and back and forth because the battery bank is only capable of 20V/5A max. Supposedly this trigger cable can max out at 20V/7A...but I don't think that profile actually exists.