I received a phone call yesterday too and it was the first I knew about it. I think I might have received a letter a few months ago but thought it was one of these extended warranty one's so I binned it. I received a letter today though so thought I would do a bit of research online.
I was also suspicious about this. Has anyone actually received a new battery and if so did it work??
The address on the letter is Advent/Eisystem REcall, PO Box 1687, Sheffield, S2 5DD for anyone who needs it, no phone number.
Still suspicious though!!!