Edit: I just realized you are talking about UK to Netherlands, so my post from the FAA is not pertinent. But rather than deleting it, I will leave it here for someone else who has the same question for travel in the US. However, the UK appears to adhere to the same limits. See https://www.caa.co.uk/Passengers/Bef...ed-in-baggage/ and expand the "Items containing batteries" section and the "Batteries (carried as spares)" section.

Up to 100 Wh per battery:

https://www.faa.gov/about/office_org..._batteries.pdf

No limit on the number of batteries, except for larger batteries between 101-160 Wh. You can have as many of these you want that are in equipment, but a maximum of two spares that are not installed in the equiment.