PowerPC :: Battery Charge Decreasing Even While Plugged In?

for some reason my powerbook battery charge slowly goes down even while it's plugged in. The power light is green as if it's fully charged but it goes down about 1% every day and then if i unplug it and plug it back in then it starts to charge, goes up to 100% like it should and then starts all over again. It never used to do this so i don't know why it's doing it now.

It started happening around the time apple had that huge recall so then i got it replaced but it still does it so it can't be the batteries fault (at least it doesn't seem likely)