I recieved one of these a week ago. I was very sceptical. Such a huge capacity increase in the same volume seemed very unlikely. However, for seventeen dollars via PayPal I figured I didn't have much to lose. It shipped from China to the UK fairly quickly, although I don't recall exactly how long it took. A couple of weeks I'd guess. It arrived in a very small jiffy bag, wrapped in a smaller plastic bag, sellotaped inside what looked like an extremely cheap iPhone cover, for an attempt at protection presumably. That didn't bode well.
The battery is very slightly larger than the stock one, so it's a snugger fit but no more than that. The stock 820 back fitted over it fine. I put it in and charged it up, fully expecting it to do nothing or set my phone on fire. I didn't have anything to worry about. It charged okay.
So how did it do? Okay, some test parameters first. I've only had time to try it over one charge to discharge cycle. I'm a very light mobile phone user. I tend to do only text messages, phone calls, a little bit of data for weather and news apps. That sort of stuff. I don't do games or video streaming. I do have mobile data on all the time, though.
Under these conditions my Mugen 1800mAh battery would last about four days, consistently. The MPJ one under the same conditions? A bit over five and a half. I couldn't believe it. This thing does what it says on the tin. The increased longevity it gave my phone fits in almost exactly with its claimed capacity. How often does that happen!
It's early days but so far I'm dead impressed. The caveats I laid out should be borne in mind. Games might kill it. It might flake out over very few charge cycles. That said, on its second cycle the battery indicator is so far implying a similar performance to the first. If this battery lasts it will transform the 820. MPJ also offer a good deal on two of these with a wall mains charger. I'll keep you all posted on how things go, as I'm sure others will when they get theirs.