I have a mixed loss (BC) so my MPOs are pretty high in my right HA compared with what my audiogram shows, I’d be surprise if there was more than a 15% difference with yours. That’s a highly uneducated guess though!
My only evidence about it not hitting the battery is that my left ear is much better than my right but the battery drain in both HAs is almost identical. I also moved from a power receiver back to a medium receiver and saw no change.
My Paradise 90 Lifes had slightly worse battery life but by about 45mins. There can be quite a lot of variation in lithium batteries probably more so in these tiny ones, it could just to be down to chance.
The deal with running batteries empty is way more important with NiCd or NiMh which have a ‘memory’ and like been drained every now and then. Car lead acid batteries, for example, hate it.
I don’t think that it’s a big deal with Lithium rechargeable batteries, but in theory you are only meant to get a certain number of recharges before their capacity falls off. The logic goes that you might as well use a decent amount of the charge (down to 20%) before you recharge so as not to waste long-term battery life. It’s also not recommended to over discharge one but the charger and HA handle that.
This effect may or may not be significant, it’s always hard to tell until you’ve run the experiment for three years!
Long story short: I think that you’re fine not to discharge them all the way.