[Galaxy Note 4 Q&A, Help & Troubleshooting] pistavampire:
Hello everyone.

(Please excuse my lengthy post, I had a lot of details to share. Thanks!)

So I recently bought N910C from a guy in Dubai, who gave me an extended 8500mah battery along with it, and claimed that it would last me 3 days easily (though later he claimed that it runs a day on full use, and 2 days no mild usage. Also claimed that standard 3220mah battery lasts less than 6 hours) but 8500mah would take around 6 hours to charge (it takes me 1.5 max, does 1% in a minute, with quick charger). I was however instructed to calibrate the battery properly, which I did, twice, tried the manual (draining and full charging) method, and also tried two apps: Battery Calibration and Battery HD.

Facts:

After buying, I flashed marshmallow stock rom for N910C and rooted with CF-Autoroot.

I have been using its own fast charger throughout, not the standard charger.

Here is the problem:

Before rooting and changing the rom, the battery was barely lasting and would shut down when around 30%. So I rooted the phone and did the calibration (manual+Battery calibration app), but the battery timing remained the same, or maybe increased slightly. The good thing was that it did not shut down at 30% and went down to 1%, where it stuck for good 15 minutes (with me browsing the net).

After I recharged it, I tried Battery HD app, which ran tests and gave me the following figures of battery usage:

30 minutes on internet: 5%

30 minutes on video: 6%

30 minutes on music: 2%

After this process, the battery again collapsed in its 30s%. I tried the battery calibration method again, but no luck now, battery collapses in its 30s. The guy who I purchased it from keeps sharing the snapshot and claims it was working fine before.

Now my questions:

I read some guides, including topics on XDA that suggested that Exynos drains more than snapdragon. So should I try to make a switch to a variant of note 4 with snapdragon, or would that make no major difference?

Is this battery faulty and I should change it? the Seller claims that he had to come on to an extended battery cause the standard was ****, so I shouldn't try and get another, it would be a waste.

What could be the problem if the battery falls in 30s% even after calibration, with exception to that one time?

Also, when it collapses in its 30s and I put it to charge, the screen shows "charging at 45%", why is that?

Lastly, I read here on xda that zerolemon extended batteries require the standard charger as the quick charger would give **** time and would charge them quickly. Will that apply to me as well? Although my battery isn't zerolemon, it's some unknown brand. And it seemingly charges quite quickly with the regular charger as well (when the phone is turned off).

He claimed that it should take my phone 6 hours to charge, it takes me barely 1.5 hours even on the extended battery, is there something I am doing wrong?

If you went through all of what I wrote, thank you for being so patient! So now, do I have any hope with this phone or should I just sell it off and maybe get an AT&T or T-mobile variant?

Thanks in advance for the guidance to come. I'll keep updating this post with whatever other tests I run, and the progress.

Khurram