Where have you purchased your replacement batteries. Sadly, there are still lots of poor quality batteries out there.
Use a battery utility, such as [http://www.coconut-flavour.com/coconutbattery/|coconutBattery] (for Mac) or [http://www.3u.com/|3uTools] (for Windows). Anything less than 70% of design capacity will require replacement.
You can also use the Battery Health Diagnostic (Settings\Battery\Battery Health) in iOS 11.3 and above. It will tell you what the health of the battery is.
If you have access to a [https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=USB+Ammeter|USB Ammeter], you could use that to determine if the phone is really drawing current when it says it's charging.