Samsung Galaxy S2 new battery dying too quickly I'm trying to figure out if the new battery is faulty or if there could be something else causing the battery to charge the whole night and then die after half a day.

If I take out the charger while the phone is off it will keep lighting up and showing the charging battery animation even though it's not charging. If I try to turn it on while it's doing this then it won't turn on unless I put the charger back in.

I'm not sure if there's a way to test if it's the battery or something else though?
I dont know if you overclock you CPU or something like that.. Or if you have custom rom or stock..

If you have root, you can use battery calibration app which
remove batterystats.bin file and your OS generates new one.

It will help.
Your phone thinks that you have still the previous battery. Calibrate it.
I had same issue on my Galaxy S3