Inferior batteries in repaired phones

I repaired one Samsung phones screen and one Samsung phones battery, the phone with the screen was basically new. I asked for only original parts for both phones. The screen was satisfactorily fixed I have no problems at all and am happy with the screen but I never wanted that phones battery replaced and it seems like they did because both the phone with the battery replacement and the phone with the screen repairs batteries die at 40%. Very bad batteries. Why my new phones battery would die at 40% as well as the older phone with the battery replacement is fishy, did they swap out my new battery for an inferior batter, also the swapped battery is vastly inferior to the original even though I insisted on original parts and paid R850 for that battery. I saw the packaging of the replacement battery it said original but there's something seriously wrong with their batteries if that is original. Other than this the service was fast and polite, I tried phoning them about it but phone doesn't seem to work, maybe number on internet changed.