does the power adapter affect battery life?

hi, ive had my mbp13 (mid 2009) since sept. '09, but i also recently (9 mos) bought a new battery for it after the old (the original that came) was no longer good. however my battery life doesnt seem to be long, in fact its the same hrs (3-4) held as the old one died and have calibrated the new one several times and ive been quitting the apps not in use, still the same hrs. so im guessing either my original power adapter is affecting it or maybe the amount of memory ive used. can anyone please help me get back to my 7-8 hrs of full battery life? thanks.