You make good points.
Even if the manufacturer limited the charging capacity to 80% having some sort of indicator that told you how you’re doing on projected battery lifespan would be nice. If nothing else, it would give you an indication of how fast a battery was heading south. Otherwise, I guess you can guesstimate by how many hours you can go on a charge as time goes by - not as nice as if the phone app just gave you some info, like I think my wife’s iPhone does (she and the iPhone are in Hong Kong right now so it’s kinda hard to check - I’m at home with the cat! She’s visiting her 97-year old father.)
I guess the Quattro battery terminals are inaccessible as it’s probably inductively charged but otherwise by reading the voltage across the battery terminals when “fully” charged, one might determine if a battery was charged to some limit less than 100%. According to AccuBattery, it’s even better to charge to a lesser percent charge. The app claims from Li-ion battery research that if you only charge to 60%, you can extend the lifespan of a Li-ion battery by a factor of 5. So if ReSound has already set a charging limit to 80% of full charge and you get 30 hours of battery life, if I charge to 0.8 of 80% or 64% of full charge, I will be extending the life of my Quattro’s even more while still getting 24 hours of battery life. So it’s just a game for me to see how long, if I follow my scheme, the dang things actually last.
I’ve heard that NASA has extracted up to 10,000 cycles out of Li-ion batteries by incrementally charging and also with help from the very cold environment of space, where you actually have to heat the batteries to avoid freezing (batteries on space vehicles are the ultimate form of the “irreplaceable” battery so NASA wants to max out lifespan).
I’ve heard the same about electric car charging, too, and it’s too bad that computer and cell phone companies don’t let consumer implement such strategies. Especially with wireless charging coming along where you might have a charging pad or charging stand that you just rest your phone on when you’re not using it, no wires to plug in or unplug, it shouldn’t be hard to incrementally charge your phone throughout the day at work or home. I think I read that American telco’s were backing a different charging standard than the Qi charging standard and that’s why there hasn’t been one standard up 'til now that would allow charging pads a whole bunch of different places so it would be easier to incrementally charge your device on the go, too, with no electrical outlets for a curious kid to zap himself/herself with by fooling around. Maybe now that Apple is offering wireless charging by the Qi standard that will carry the day and the other standard will be history, if it isn’t already.