Bloody hell stubbs, one time then thrown, i get about 4-5 outings with mine, and i find that they usually start to play up abit before they pack up, giving me enough warning to change them, but everyone to their own mate, fair play.
as I said, it works out to around 16p per battery, 32p per collar x 4 collars = £1.32 per outing, if I was ferreting a sat/sun, then yup Id probably use the same ones, but mostly ferret every other weekend, in which case, I bin them