New charger causing problems with battery and overheating.

So, recently the charger that came with the macbook i bought in october 2011 had to be replaced because the cable was splitting near the connector. I bought a new official apple one, but i've noticed that it takes much longer to charge the battery. I plugged it in at around 11am this morning and it hadn't reached 100% charge until about 6 or 7pm. I unplugged it from the power source about 10 minutes ago and the battery has dropped to 88% already. I also noticed that for long periods of time whilst it was plugged in it would display the (not charging) message. My laptop has been on all day, but the lid hasn't been open, and it feels very hot and i can hear the machinery inside whining. I have never had this problem before buying the new charger.

Does anyone have any ideas why this might be happening?

( also, just noticed that my battery level is at 80% and it says i have 1.25 hours remaining!

i'm not running anything that should be draining the battery this quickly! )