Smart battery case - how it really works ?

I recently bought a Smart battery case for my iPhone 6. While I am fine with it's battery life as I'am not a heavy user, I like the added rugednes and convience.

The problem I have with my smart battery case is that I really expected a "perfect" accessory for my money. I was nicelly surprised with It's feel and fast-charging capabilities, but one problem is rather glaring to me. The case drains. While the iPhone can withstand days of non-ussage, the case quickly fills the iPhone to 100% but after that it looks like it continually leaks current somewhere.

I think that iPhone manages every joule of power with precission so it should not use much power directly from the battery case at stand by. Still case drains with rock hard regularity at 2% per hour which I find very high, when not used. That's some 20% trought the night, and some 48% percent per day.

That means that if I drain my case in 24 hours, potentially half of case power was bassically wasted out and it could last me a very good part of the second day if preserved. I found myself that I can noticeably increase the battery life of my combo, by putting the case off every time I don't use the phone - super annoying, but equivalent to pushing the "off" swith on those other cases. Even doing this before sleeping helps a a lot.

What's the most perplexing, if I put on a somewhat charged case on an drained iPhone, and plug them to a regullar 5W adapter when the phone reaches close to full cahrge (~90%) the case lost some 3-4% percent in some 2 hours time like always. I don't think the case provides additional power for faster charging, because it would deffinitelly drain faster doing that and the phone charges just as fast, if not a tiny bit slower compared to charging without the case. But where the power gets lost then ?

I actually think it's a deffective behavior, according to my knowldge when iPhone gets full charge, it stops powering the battery while using all charger power to power itself - so almost all power that dissapears from the case should be used up by the iPhone, not even mentionig that "drain while charging" issue. It might be a software issue too, possibly getting fixed with an update.

I also experienced confused power indicators - chaotically jumping, changing and stuck percentages shown as remaining charge, but those do not affect the total endurance, when using the case.

Have you experienced a similar problem ? How does your smart battery case behave in your experience ? Is it possible to limit the drain in some way ? Does the iPhone 6S plays nicer with the case ?

iPhone 6 + iOS 9.3.1 + Smart Battery Case