So, I got a new battery for my iphone6s. Yes an old phone and I do not need more.

My phone wasn't holding much of a charge and was juicing out quickly and since giving my new battery I did make it to 50% by the end of my day, work shift where I talked on the phone, did some text and looked at FB. But still it seemed to me when I first got the phone it lasted longer. Significantly longer. Why does it not feel like me paying for a new battery gave me all that or is this just a norm.