I bought HTC10 on Sep 2016 which support QC3.0 and Huawei Mate9 for My father on Dec 2016. Both phone were charged usually every or alternate night. 2 years later, the mate 9 battery is still holding on well, not so much for the QC3.0's HTC 10.
I believe the Supercharge's 5V charging voltage help retaining the battery health. My HTC 10 used to left with half of battery life when I reached home at 5+, but now retain only ~30%.
The 40W supercharge of 10V/4A probably won't keep the battery health as good as the old 5V/4.5A, only time can tell.
This is very misleading as the phones are used by 2 different people with different habits. The battery capacity are also different so how can you compare apple and orange?
Based on your post, a few points to note:
1) the phone that charges the most will wear faster (if consider mAH charged remains equal)
2) the phone with better battery life (considering mate 9 here) in theory charge lesser times with the same amount of time used so it should wear slower than
3) I would suggest u to download AccuBattery as it gives you great insight about batteries and it also tells you how much your battery has worn over time.
4) research found that charging the battery to 100% makes your battery deteriorate much faster than charging to say 80%. Again, AccuBattery shows you the battery wear cycle and explain some of that.
5) based on these info, to keep battery in good condition, one should do smaller charges say 40% to 80% instead of charges from 10% to 100%
We all know heat is the biggest killer for batteries so keeping it cool can ensure your battery is kept in good condition. If you find your phone heats up quickly and reached high temperature, I would suggest that you check what went wrong (some people like to play games and charge at the same time that caused the phone to be very hot) as prolong charging in this way can kill your battery very quickly.
In quick charging theory, imagine you have to feed 1000 people that queue in a single line vs feeding the 1000 people with 10 lines of queue that would be 10x quicker right? So the fast way would be able to hit different cells at the same time so they get charged simultaneously instead of a single point charging while monitoring and maintaining heat control.
Having said that I disagree 10v/4a charging will damage the battery quicker than 4.5v/5a charging considering they implement the monitoring control well
