Long story short: nowadays 65W-capable USB C powerbanks make more sense in my opinion, than multiple Thinkpad batteries. And they work with all laptops.

Yep just like the S versions they have a double battery. This is great because the total can get close to 100Wh (when using the 72Wh external) but hot-swapping requires an internal battery in good shape which is not so easy to come by. From Lenovo they can be very expensive or not available. From third parties you're always gambling that those batteries will play nice with the proprietary Thinkpad EC.

I bought both (3rd-party) batteries for a T440S, and the internal would suddenly show up as 0% every couple of weeks, and had to be "reset" by opening the base, unplugging and plugging it in..in the end I just put the original internal back; the external has been amazing instead, and it does basically all of the work since it's the 72Wh version. Fun fact: these laptops work perfectly with only one of the batteries attached.

All thinkpads (at least all T series) have easily swappable batteries. The T480 has 2 batteries, one external and one internal. Older models had only external, newer models have only internal. The only advantage of the T480s battery setup is that you can get 100 watt hours in the laptop. The gen that came out right after it only has like 50 or 60, but I think the T14 gen 3 and newer machines have bigger batteries.