Plagued by the same disease on Nexus S, stock 4.0.3,
i9023XXKI1, IML74K. purchased it ~1yr ago from vodafone, all went fine until 3-4 days ago when i noticed the battery is discharging way too fast though i'm not doing anything "unusual".
today if finally had the strength to "tell" me it won't charge anymore so i set sail around home port in google land which brought me here , here's my latest story:
put it into airplane mode so it's not connected to anything, display settings on "auto".
plugged in wall socket it charges up to 75%, seen in settings\battery where it says "charged" while the battery icon in the status bar still shows the lightning bolt and approx 2/3 charged. so i keep it plugged in some more time, but now it says 86% percent "discharging" while the status bar icon still shows the lightning bolt.
about 20 min later it says 95% "discharging" but now there's no lightning in the notification bar and the battery icon is being shown as completely full (blue colored if it makes any difference).
while i typed the above it went up to 100% "discharging", the icon still full in the notification bar.
android OS 49%
android system 10%
it also says 8min43s on battery which should mean it actually disconnected itself from the charger (which remained plugged in at all time) around 8min ago.
the battery level does not decrease, it's still 100% "discharging".
Thanks for any useful piece of info you might have :)