Battery not holding charge long

Yes, this phone is a few years old. But still works okay! Battery was not holding charge - so with much effort (someone at the factory tweeked out half the screws and they couldn’t be removed) I replaced the battery with a new one from iFixit. Battery performs by not like the original. New battery barely holds a charge for a day. Could get 2 days out of the original. Suggestions on how to get more time on a charge?