I've been using a 3300mah 3S Protek lipo in my 3PK for 3yrs this spring. No issues at all. I looked at it yesterday and it was at 12.2v from the last time I charged it about 3weeks ago. 3S fully charged will be 12.6v and mine has not had any probs with the full voltage.

I also run one in an older 3PJS and haven't had probs with it either.