I looked at the ZeroLemon but it WAY TOO FAT and bulky. I bought one of these instead. It's a 7,600 mAh battery (and case) that is WAY slimmer than the ZeroLemon and has a 2 year warranty!

https://www.amazon.com/gp/product/B00JQZ9394

You can also find it on AliExpress direct from China.

https://www.aliexpress.com/item/High-Quality-7600mAh-Extended-Battery-Black-Door-Cover-Case-Extended-TPU-Case-For-LG-V10-H968/32664834434.html

I've been using mine for 3 charge cycles and battery life keeps going UP. For example, using my phone at work all day listening to music and checking emails and text messages, when I left work it was at 99%! It's now after Midnight and it is at 80%. Granted, I use an awesome battery saver called LeanDroid that does a fantastic job of keeping my phone in deep sleep (I'm on Lollipop so no Doze mode). I have it wake up and check for new emails and such every 30 minutes. Oh, and I have my brightness at 90%. Yea, super bright, I like it that way. Just make sure you break the battery in by using it until it hits 0% (or the phone shuts down) then charge it for 10 hours with a good charger and repeat this cycle 3 to 5 times. Hope you guys find this helpful. Cheers!