Hi Lucy,
You're still lucky (hehe, I crack me up), that your shipper is collaborating, although they should have been aware that loose batteries wouldn't pass the postal Nazis, I mean, hard working civil servants of course.
There are no fully functional original Ugobe NiMH batteries (that haven't been repacked by a previous owner), so any second hand Ugobe will have this issue. That is why the majority of them are on sale, "my Pleo just says huh and goes to sleep!", or "my Pleo runs for 5 mins and then goes to sleep."
You get the idea. Not too many people bother to replace the battery, i.e. they can't find one on Ebay, or little Susie or Joey is now into Instagram, Fornite, or college.
But you, the Pleo adventurist, know about battery repacking, so all is well, undaunted, you move bravely into the future to face the challenges ahead!
Cheers!
Peter