i've never had that many in one "session" at any time. four or so is the absolute limit. for me they actually get almost painful. wait, no that's not it. not painful, really, but they feel like i hafta pee really, really badly so maybe the best way to explain it would be a sharp, tingley pressure. either way, they start to slide towards the not so good side. i'd chaulk it up to serendipity and make sure you keep a good supply of batteries on hand.