This has come up from time to time, and with units like the TP-Link often not supporting even minimal builds due to 4 or 8 MB of flash and limited RAM, the "what do I do now" question doesn't seem to have a cheap, one-stop solution.
The good news is that there are a couple two-step solutions, with the popularity of cell phones.
Step 1: Buy a USB-style "Power Pack"
I used to try to keep track of whose were good and whose sucked, but the ubiquity of 18650 LiIon cells on the market have driven the cost of these down significantly. The two-cell units advertise somewhere around 6000 mAh and are available from recognizable manufacturers for around US$20.
6000 mAh seems a rather generous comparing with the test results of the best of the 18650 cells. Claimed 6 Ah * 5 V = 30 Wh. A single cell with a 3000 mAh capacity to 3.2 V is more like 11 Wh * 2 cells ~ 22 Wh. Then you've got converter losses. I'd figure more like 20 Wh (or less), or about 4000 mAh, to figure run time. If run time is more important than size/weight, consider a three- or four-cell unit.
Best thing is you can use it to charge your phone if you need to. Unlikely a travel router can get you out of that jam!
Step 2: Buy a 5-V Travel Router
2.4 GHz Only
Right now, for me, it's hard to beat the GL.iNet AR300M-Lite at under US$20 for size, weight, or performance for a 2.4 GHz unit. Its major drawback is a single Ethernet port, which doesn't seem to be a significant limitation for travel use.
As a bonus, the GL.iNet software is closely based on OpenWrt 18.06.2 (as of early 2019) and includes many preinstalled features valuable to the traveler, such as managing captive portals, wireless repeaters, VPN, ...
I measured the power draw of these a while back at under 300 mA with a client connected. Figuring on 4000 mAh from the pack, that's over 12 hours of run time.
At US$40 for both, for a current device with 16 MB of flash and 128 MB of RAM, it seems like a significantly better option that trying to shoehorn things into an outdated TP-Link or similar unit.
If you need 5 GHz, my preference is the GL.iNet AR750S. Not cheap at US$70, but I'm very impressed by the build and performance. A dual-band unit runs two radios, and will draw more power. The AR750S, between its faster processor and two radios runs around 400 mA idle, so you're around 10 hours of idle there off the pack.
Same great GL.iNet firmware based on 18.06.2. Good enough that I have one of mine still running it for when I travel.