A:Answer I've been using this case for several months and have had slightly better results than you report. I don't get a full charge from 10 to 100% but I usually see at least a 70% increase in battery depending on use while charging.
The biggest reason you're not getting to 100% is that the battery in this case (2525 mAh capacity) is smaller than the battery in the iPhone 7+ (2,900 mAh capacity). This means that best case scenario, if 100% of that stored energy is transferred, you'll see an 87% increase in battery.
Realistically, you're only going to see close to that if you turn your phone off and don't use it while it's charging, and that's assuming the battery case can still hold that full charge and nothing is lost in the transfer. As it's charging with the phone still powered on, the battery continues to deplete, so it may actually be giving you that 80% increase, but you may be using 30% of your battery during the charge time. (You could test this out yourself by depleting your battery to 5-10%, turning off your phone, letting the case charge it fully, and then turning the phone back on to view the results.)
If your primary need is battery life, I would look into something with a larger battery or consider carrying a power bank which you can easily get 12,000+ mAh (3+ full charges) without breaking the bank (no pun intended). Personally, the extra 70% or so I get from the case is enough to get me through most any day of fairly heavy usage. The ease of wireless charging also makes sure it gets topped off regularly as well.
