I happened to be on the Ray-O-Vac site now for a different reason and saw that in their Hearing Aid FAQ (select Question #2 after clicking this link)
Ray-O-Vac says that once the tab is pulled, sealing the holes again does not slow battery depletion. Of course you could argue that Ray-O-Vac may not be the most objective adviser on this point.
Hey, if it works for you, keep on keepin’ on, or sealin’ on, or whatever. I suspect you’re right that that there may be enough oxygen to keep the battery supplied with air in the overnight situation where I’m not using a resealed battery, whereas if you seal them up for days at a time, it may have a more noticeable effect.
Other things I learned watching the video at http://www.rayovac.com/en/Products/Hearing%20Aid :
Battery life can be a bit shorter in one aid in one ear, if your hearing loss is worse in one ear compared to your other ear. Things that can shorten battery life: setting the gain higher, using the aid in noisy environments such as restaurants or concerts, heat (this would include leaving a spare pair of batteries up against your body), cold (storing batteries in the refrigerator) humidity (either high or low), leaving the battery inside the aid when you put the aid in a Store ‘n’ Dry type device–they recommend not just opening the battery compartment (obviously) to stop battery drain but also not putting the batteries in the dryer device, because dehumidifying your batteries or using them in dry arctic or desert environments can drain batteries faster just as high humidity can.