I've had the battery for most if this week now and here are my thoughts -
Battery purchased:
Ebay 3800mah extended battery made in china
Price:$15 shipped
My daily phone usage: light screen use; 30-45 min of voice; 40-50 texts; 30-45 min of web browsing; 1hr pandora, 3hrs music from sdcard. Syncing 4 emails on push sync; facebook, facebook messenger, twitter, linkedin, hootsuite all running in background. Wifi, 4g, gps always on. I don't use airplane mode at night or anything like that, and I don't use Juice Defender, DS Battery Saver, or any other battery saving app.
Thoughts:
In short, worth it. My phone life might not be doubled but it is definitely longer. With the stock battery I would unplug it from the charger at 5:30 am and it be dead by 6:30pm. This battery seems to be making it to 10pm (end of the day for me) with 20+% remaining still.
Monday - the battery arrived around 11am and I just threw it in my phone, it came out of the box with 71% charge so I ran it for the day. It made it to the end of the day with around 25% remaining so I left it off the charger for the night... I wanted to completely kill it.
Tuesday -at 5:30am it had 4% remaining so I put it on the charger. Unfortunately the day didn't want me to get a proper full charge to start the day so I ended up on and off the charger all day with way above average use.
Wednesday - first full day... had above normal usage - 1.5hrs of Nav usage and 2+hrs of voice added to normal use. Battery seemed to drop at normal
stock battery rate. By 6:30pm I was under 10%, but I kept it off the charger. I noticed it dropped down to 3% then went back up to 7%... finally died by 9pm, so I put it on the charger for the night. Flashed cm10b6 during charge time.
Thursday - second full day...above normal usage again, only mildly tho - 30min of nav added in. Made it to the end of the day with over 30% remaining, so I left it off the charger for the night.
Friday - woke up 4:30am and found lots of emails and texts received and a battery at 3%. Put it on the charger til 7:30am to get full charge. Above average use day again - 1.5hrs of wifi tethering, flashed twrp and created a backup, 2hrs of web browsing added to normal. By 11pm I had 20% battery left (remember it came off the charger 2hrs later than normal tho) so I just left it off the charger for the night.
Saturday - woke up at 7am, battery dead so its currently on the charger.
Afterthoughts: I thought I would hate the added thickness of the phone but it really doesn't bug me at all. This battery is great, especially for $15. The only thing I can figure (this is "the cup is half empty" thinking) is perhaps they have a crappy quality control system in place, so people will have higher chances of getting a bad battery... but so far I think everyone here that has gotten one likes it.