[Samsung Galaxy S Relay 4G] pianoplayer88key:
I've had 2 of the EZOPower 4100mAh batteries, and am experiencing the same problem that stonefoz mentioned about the batteries swelling. In my case, for example, the current one has gotten to where the cover will just spontaneously pop off, and the battery will dislodge, forcing the phone to lose power. Also, regarding his "staying warm" comment - sometimes when I was doing something extensive on the phone, it'd sometimes get so hot, especially the keyboard area, that I could barely hold it, and that concerns me some.

I believe the second one has lasted longer than my first, though. It's not quite as bad now as my first was when I replaced it. I bought my first one May 18, 2013, and my second one September 18, 2013, 4 months later. It's lasted till now, May 7, 2014, 7 and a half months later, but it's about time to replace it.

It looks like it's no longer available, but I was thinking I should try a different one anyway.

One option is this 4600 mAh Mugen battery for about $90, and another is this 5000 mAh MPJ battery for about $35. The MPJ does say it's only 3.7 volts, which according to scaltro could be a concern with longevity per charge.

I definitely would like better battery life. I've noticed that playing FarmVille 2: Country Escape is quite a drain - I'd go from full battery to getting the low battery warning after only something like 2 to 3 hours or so, even with the EZO battery. Earlier, I popped in the factory Samsung battery, topped off its charge, then decided to test battery life playing FV2. I also turned on bluetooth (and sent the sounds to an external speaker), cranked the screen brightness all the way up, and turned off power saver mode, in an attempt to get a "worst-case scenario". I tried turning on WiFi (we have a hotspot here now) but it wouldn't connect to the game server, so I just went through my unlimited+unthrottled 4G. :)

The results:

2:45am - battery full, unplugged

4:15am - battery 22% (I checked it a few times along the way periodically, but neglected to note the times)

4:23am - battery 14%, had just gotten the battery low popup warning

4:33am - battery 5%, battery critically low popup warning

4:35am - battery 3%, then I went and plugged it in.

So, it lasted only about an hour and 50 minutes from full to 3% remaining. I'm hoping a good battery would be able to go all day and all night and into the next day with similarly-intensive use. (No I wouldn't be playing games the entire time of course!)

Personally, if the $35 MPJ battery would be good enough, and significantly better than the EZO, I'd prefer to go for that one.

I'm wondering, though, if the $90 Mugen is a huge leap up in quality, though (disregarding the NFC for now which I haven't had to use)? It's a bit rich for my blood to drop all at once on a battery for a phone ... BUT, their website tells me they accept returns up to a year later (and I've gone through TWO EZOs in that time), which gives me some hope. If, overall, I'd be spending less by getting one Mugen and it outlasting 4 or 5 EZOs (if they were still available), I'd get that.

On a side note, it'll be a while before I can afford to replace my phone, but when I do, I'd really like a good QWERTY keyboard. I see that very few phones come with them now, though, and the ones that are are near the bottom of the barrel spec-wise. I'm thinking I'll need to get an external compact bluetooth or USB keyboard with my next phone, and expand my options for the phone itself. Ideally I'd like to get one that I can put in a flip case, with the phone in the other side of it, and close it when I'm not using it. (Although, there is the concern with getting the phone out quickly to answer calls, although I maybe only talk 25-50 minutes a month or so.) Any suggestions on what to look for in the case/keyboard department, for example? Chances are it won't be till 2015 at the earliest (and my wallet hopes my Galaxy S Relay 4G will last through 2016 or so unless it dies or something else goes seriously wrong) before I get a new phone, but I like to start my search early. When I do get one, I'm hoping it'll last at least 4-5 years, and maybe stretch it to 7-10 if I'm pressed for cash then.