The samples are categorized as electrically driven vehicles, batteries fitted. I think it may depend on the size of them these being larger than the smaller type fitted to electronic devices. I have come across this problem in the past, for instance DHL will handle uncharged batteries with a certification for this product type, but they need to be packed individually. Some suggestions were leave the batteries out and buy as separate in the UK but that works out quite expensive, especially for the latest technology available in large lithium batteries. Even so, air freight was going to be expensive, especially considering the small amount and value of the samples in the first place. Of course surface freight is slower, but time is not a pressing issue in this case.
OK and thanks re the FF advice, appreciated
JonO