Since Purism can’t ship replacement batteries outside the USA (except when ordered together with a new device using the same battery, which is not possible for e.g. a Librem 13 battery since they are not making the Librem 13 any more) I looked for other vendors who might be able to provide compatible batteries.
The original battery in my Librem 13 v2 had a “Product ID: TU131-TS63-74” printed on it so I searched for that text online. There seem to be two different batteries with the same part number - a smaller one with 24 Wh capacity and a larger one with 45 Wh capacity. The original battery has “Capacity 45 Wh, 7.4V” printed on it so I made sure to order that one.
The exact product I ordered was DELL XPS 13 8808 U13S881 U33X UX32K TU131 Battery - BatteryMall.com but there are many other suppliers offering similar batteries also claiming compatibility with the same part number.
My order arrived last week and I installed the battery yesterday. So far everything seems to be working fine. So I would suggest a similar approach to anyone else outside the USA who is looking for a new battery. If you have something other than a Librem 13 v2, make sure to open the case and look at the part numbers printed on your battery first so you can order the right one.