The description to this suggests that this game was sold as a full deck.
I don't remember ever seeing that during my Monster in My Pocket obsession, however what I do remember is that packages of the monsters used to come with 1 card. What I remember of these is that they were much like Top Trumps, which sounds very similar to how these are described.
So, is it the same game?
Now I'm thinking about it, I think I need to go find my Monster In My Pocket Cauldron and see if the cards are still in there - if they are I can see if they're called Battle Cards or not...
Answering my own question - I've been up in the loft and they are indeed the same. So cards that came in booster packs were all part of this game. However it looks like the majority of my cards (the series 2 ones) actually came with my cauldron - didn't realise that until now!
Am going to keep these cards out and play it again soon and see what I think. It is definitely a very simple top trumps mechanic, but it could still be fun. I have also taken some pics which I'll be uploading as there are currently not for this game - criminal!