I got this
https://www.amazon.com/gp/product/B06XRN7NFQ/ref=ppx_od_dt_b_asin_title_s01?ie=UTF8&psc=1
And it has been working well for me for a couple months. Make sure to read up on which direction turns the voltage down.
My multimeter is only rated up to 20 volts, so i had to turn my buck converter all the way down, then work up from there.
Do not connect the pi until you have the voltage at 5V.
Edit: i also recommend implementing a shutdown button to safely power off your pi before you cut power to the printer.
Edit 2: I also got this fan that blows on the buck converter (and into my pi box)
https://www.amazon.com/gp/product/B072FW3DDQ/ref=ppx\_od\_dt\_b\_asin\_title\_s01?ie=UTF8&psc=1
Most Lipo battery packs will be listed as the approximate nominal voltage of a pack.
For example a "12v" Lipo battery pack is usually 3 cells with a nominal voltage of 3.7v each or 11.1v total, However the full charge voltage of each cell is actually 4.2v per cell, so its really a 12.6v battery when fully charged. And when it is at a safe minimum voltage, the cells will be about 3.2v, so 9.6v total.
so really a "12v" pack is a 9.6 to 12.6v battery, depending on the charge.
If you want to replace regular AA or AAA cells that are usually 1.5v each with a Lipo pack, then it is sometimes difficult to find an exact combination of cells to hit the target voltage.
What I have done is to get a variable output step down regulator, and find a combination of Lipo cells that equals more than the target voltage I need, and then adjust the output to match what the original batteries provided.
These work well if the device uses an uncommon voltage, like 4x AA batteries would be a 6v target voltage, and that is more than a standard 5v USB. so use a 2cell Lipo pack with a nominal voltage of 7.2v and then a step down regulator to drop it to 6v total.
You can also get step down voltage regulators that will output at some set values, like 5v, 9v, 12v, and 15v if the device uses a common voltage amount.
You can also get step up boost circuits, they can increase the voltage above the value of the pack, but that usually means a trade of of less Amperage.