I think the biggest enemy of the Oticon Lithium-ion battery longevity (not the same as daily capacity) is to avoid running it down to almost zero charge where you start to hear the low battery warning chime. Topping it off for 15 or 30 minute in the middle of the day or whenever you have a chance to avoid running it down almost completely by the end of your day would probably go a long way in making the batteries last 3-5 years instead of 2-3 years.
If you wait until your battery capacity is diminished greatly after only about 2 years before topping it off some time during the day will help make it last longer for that day, yeah, that will help make it last longer, but by then your battery capacity is already diminished greatly and topping off is only a stop gap measure at that point, instead of topping off being a preventive care measure.
I think ideally, if at the end of the day you’ll mostly find your battery to still have about 30%, then it’s probably OK to not bother topping it off mid day some time. But if you only have 20% or less by the end of your day without topping in between, then it’s probably wise to try to top it off in between if you can just to simply avoid running down your batteries to too low a level by the end of the day.