Around here, they are a staple item that I can buy without worry.
I've been using the ZeroLemon 8500mAh Battery Case for 3 months now and I could not be more impressed. Now, as my Note 5 aged I noticed a decrease in battery life that most phones get around the 1 year mark, so I was looking for a battery case to extend the life of my phone until the Note 8 comes out next year (R.I.P. Note 7). Before buying this case I tried a few other battery cases, which led me to discover that most of the hard plastic cases that just clip on are all made by the same manufacture and just get different company logos printed on them. (ALCLAP 4200mAh Extended Battery Case, [...]) Every single one I tried suffered from slow charging speeds and cheap build quality.
So, I am very particular when it comes to my phone cases. One of the biggest issues with other battery cases is they're more battery than case. I wanted something that was going to keep my phone protected along with keeping it charged. I was pleasantly surprised to see that the ZeroLemon used a high quality TPU case that covers all edges of the device. The cutout for the headphone jack is big enough for most headphones (I've tried it with my AudioTechnica ATH-M50Xs and the stock samsung earbuds). The speaker grill does muffle the sound slightly, but it's really only noticeable while listening to music at max volume. The cutout for the S-Pen is huge and I rarely have an issue getting it out. The only other thing I feel should be noted about the case itself is that the camera cutout is very deep and reduces the range of the flash/light. I've only noticed this while taking pictures at night, otherwise the camera is not affected.
Now the battery itself has been nothing short of amazing. I often find myself only charging my phone once every other day now. With average use I've stretched the battery 3.5 days multiple times. With heavy use, which often included 9 hour flights and hours of the battery draining Pokemon GO, I can easily make it through 2 days before needing to charge the case. The battery also charges my phone faster than the stock charger (according to the android app Ampere Meter). Other great additions to this case are the USB A port that lets you use this case as a power bank for other devices and also the priority charging that charges the phone before the case when plugged into the wall. The back of the battery also has a battery charge indicator, to check the battery level press the button once or hold down the button to start charging the phone or a device via the USB A port. It also comes with an extra connector that connects from the phone to the battery, just in case you lose it.
The only downside to this case is that it turns your phone into a brick. It will more than double the weight of the phone. But for that extra weight you get a ton of battery life and features. However, I have huge hands and usually get bulky cases for my phones just so they're more comfortable to hold. All in all I'd recommend this case to any power users who need that extra battery life and don't mind the bulk.