I too just noticed this "issue"
as one of the previous posts said already, 4.2 or 4.25 is what I know the max for li-ion batteries for these years. When the galaxy s3 show 90% power, I take the battery out and measure it, already 4.215 volt...
So I suspect its max voltage is set to 4.3, which then would have a nominal 3.8v or so rather than the most seen 3.7v. and sure the battery's nominal voltage is 3.8 printed on the battery.
So, I think this isn't an issue but intended. am not a specialist in the field so not quite sure what chemical differences are causing this..
BTW, the galaxy s3's charging function is quite bad indeed... I've two here that don't charge while the phone is off(normal while on). one of them continually vibrate with black screen(about 1 vibrate every 5 seconds), the other one vibrate every 5s too with the gray empty battery symbol respectively. For same charging method(plug in the cable while the phone is off), my other good galaxy S3 would vibrate once, then the gray empty battery symbol with white circle inside, then a battery symbol with "green fluid" filling up inside representing the power percentage. Suspected faulty usb port.
=====
final word,
I have heard about galaxy s3 exploding while charging(yes, there are reports on the web already, just google if interested), and there are just so many posts talking about all kinds of charging problem that galaxy s3 has... I'd just charge the battery up to 85%~90% only every time to be safe lol~ if I have time, I might try charging the battery using external hobby charger so I can measure the capacity. If it needs to be about 4.3 or 4.35v to be 2100mah(confirming it's not being over-charged), maybe i could feel better then ~ extra info, looks like there are 4.3v and 4.35v 18650 batteries available too, so maybe we are just not keeping up with the new technologies
