New battery won't charge to 100%

The battery on our S5 mini was bulging and was discharging faster so we purchased a new one. When we put it in the phone it was at 50%. Charged it all night only charged to 74%. Next night turned phone off and did the same thing. We contacted the seller and they sent us a new battery and it is doing the same thing. The old battery still charges to 100 %. Could both batteries be bad or is something wrong with the phone.