Dead Karl is one of those rare and amazing but largely unknown bits of hidden internet glory, and unusual in that it was one I was not previously privy to.
I also thought the battery thing sad "MIDIUM", but it turns out that if you look closely it actually says "MIDUM" - I could be deceiving myself, but I think I'm right on this score...
Anyway, the bottom line on batteries is: get rechargeable ones, c. 2500 mAh, recharge regularly, and you should be fine.
And joeeoh, it shouldn't really make a difference, but taking the batteries out can't hurt.