I also suffer this weird battery behaviour with the device charging, it will take ages up to about 60%, and then instantly its at 100%
I also get this on the way down... when im using it, the battery drains fast, but when I get to 35 -40%, I then suddenly get the low battery 15% warning flash up, and then im all out of juice.
This is the same whether im on 4.1.2 or 4.2.2 custom or stock firmware
I rarely get more than an hour screen on time, and thats with fairly low brightness and power saving mode on
Smartphone craze started with T-Mobile G1