Theo wrote:

Hmm, 20V is a funny voltage for a lithium pack - it would seem to be
5-and-a-half cells.

Probably going by the leftpond marketing convention of 4V per lithium
cell as opposed to the european 3.7V per cell e.g.

https://www.amazon.co.uk/Dewalt-DCB184/dp/B00L8T5VJW

https://www.amazon.com/Dewalt-DCB204/dp/B00BQHLJ4M