May ruin your built in battery.
344313
Overcharged my phone, had to send the phone back in.
2071806
Be careful, this battery is erratic and occasionally just drops in juice without reason.  I've had mine for a year now and just last week I couldn't close my blackberry case and was wondering why. All the grooves in the case seemed to match..but then I noticed that my Seidio battery was slightly bloated and fatter.  I think it's gonna explode if I'm not careful.  I have put my OEM battery back in, despite the lower mAh and will try to get some replacement from Seidio, which I doubt.
4757486
I bought these for a research trip to the Amazon.  I had one of the batteries in my camera initially, and it seemed to perform much like the Canon battery.  At some point in the trip I put in the second battery, and put my camera away in my hard case.  I happened to pull it out about 20 minutes later to show someone a picture, and the entire camera was too hot to hold.  I immediately dumped the battery, which was extremely hot, and had apparently internally short-circuited.  Had I not checked the camera by dumb luck, this battery would surely have destroyed my SL1.  Inexpensive, yes. Cheap, yes.  I will update this review depending on their customer service.
518173
Worked briefly at first, now it's so intermittent, I can't trust it to be safe. I have tried multiple types of batteries, including brand new or freshly charged. Sometimes it starts alarming just sitting on the desk, so I had to take the batteries out. I've been shocked too many times to mess with this.
762338
My battery had gotten to the point where it would drain after just a couple hours of light use. I had to heavily rely on external batteries and being near outlets. I decided to try replacing the internal battery after I saw that it would cost less than 20 bucks. My phone warranty had already expired, so I took the risk.

The original battery at the time of replacement had 692 cycles and 982/1430 mAh. This new battery after installation had 1395/1430 mAh at 0 cycles. I'm disappointed it is not the capacity advertised, but I guess that's what you get with cheap knockoff batteries.

Some tips for replacement:
Watch a few videos on youtube before you begin
You will probably need a suction cup tool made for opening phones. The suction cup that comes with this kit is very weak.
Use a small dish to keep track of your screws as you take them outthey are TINY.
Wear gloves and keep away from dust to keep internal components as clean as possible.
Beware the adhesive on the battery. You may need to pry quite hard to get it out. I found the guitar pick most useful for this. DON'T puncture or break the battery.
Keep the two halves of the phone steady at 90 angle or less to prevent damage to the display cable.
1534980
It works great, but if you connect the charger, unplug if you don't see the battery icon. Makes it hot and won't work anymore. I had to learn twice.
4454652
This device has a major problem, batteries that are discharged below .9V are not recognized and cannot be charged.  So if batteries get fully drained, you will be unable to charge them.  This forces you to buy another charger (not all chargers have this limitation) or throw perfectly good batteries away.  Not sure how this slipped by so many reviewers.........
1058036
We used this in our shop which it worked great for a while. But one day we pulled it off the charger and right after pulling it off the charger the battery  swelled up and blew up in one of my co workers hands and shattered the case. Was extremely dangerous BE CARE FULL and they won't take it back!
1621564
This case was absolutely amazing when I first got it. Then when I went to charge it that night I realized how irritating it is to open the charger port on the phone with the case on it. Then the next day I went to work and checked my phone to see my battery had dropped 20%. I assumed my phone was just having problems until I noticed an icon saying my phone was overheating and that the phone was taking measures to cool it down which was killing my battery. I would not get this case if you live in a hot climate area because, of this issue.
4763467
For a battery case, it is ok, but since this is not a QuickCharge case, it pretty much can't charge your phone battery whatsoever (unless the phone is off, I guess, but who does that?).  It can typically provide enough juice to prevent the battery from discharging, but I haven't had the phone battery gain more than 5% charge by the time the case is empty.  Charging both your phone and case at the same time will easily take 6 or more hours.

All this would be acceptable since it does a pretty decent job of extending battery, but it has one major, glaring flaw that is completely unacceptable in my mind.  Regardless of whether your case was already charging your phone or not, when you plug in the case to charge with the phone in it, the case starts charging and the phone stops charging.  Even once the case is fully charged, the phone still won't begin charging unless you press the button after plugging it in.  This will allow both to charge simultaneously, but if you forget to do this when you plug in your phone before bed, you will end up with a fully charged case and a dead phone.  This also means that the charging cradle I use at work is completely useless because I can't get to the button once it's docked, so my phone will never charge in it.
3308206
Works fine on 2017 MacBook Pro 13 BUT the problem is some rechargeable batteries like the PowerEx AA NiMh batteries I used don't fit the battery compartment. If you try to force-fit the battery, then good luck getting it back out. This is a design flaw. Width of the battery is fine, but the length for the AA battery is too short- by quite a few millimeters. The designers could have prevented this problem by allowing some elbow room for the wire spring terminal on the negative polarity side. This would provide extra space for the battery to fit with no problem. See the photo showing how the length for AA battery is very tight. This is a brand new PowerEx AA rechargeable battery that is now damaged because it took a screwdriver to pry it back out of there. Buyer beware!
1685904
external battery has over heated my iphone and the USB cable. this could cause damage to my phone.
Battery should be checked for faults
1191123
When I first started up my Aria, I noticed that the bottom was very hot.  I opened up the battery case and found one of the batteries so hot that it had partially melted the plastic housing.  I removed it and it split open.  I put in new batteries and was concerned that there was a short in the item, but the item worked properly after that.  Chalk it up to a bad supplied battery.
4234447
This battery has a possible open. While charging the red lite flashed indicating charge coming in with no battery, yet batt. was installed.  Camera was dead. Removed battery, and charged it again.  Now it seems ok.  Other review complained of a short life. Would recommend to avoid this battery.

Rocky
2043270
If you can charge these with your camera somehow (I can with my Video recorder), DON'T.  You will not properly charge the batter and you won't get the same run time on the battery!
2462167
Cheap battery is a danger to equipment and people. Acid leak killed my camera and gave me a terrible rash.
1015077
Seemed OK at first, but one of the two I had died after a few months intermittent use.  When I opened it up the control board had fried.  The internal wiring isn't particularly good, it has 4 18650 cells wired in parallel with two strings of two.  If there is a cell imbalance then it'd be easy to fry the batteries.  The USB outputs are wired in parallel also.
It's not all bad though, I'm going to reclaim the 18650 cells for another project.