Replacement Battery Worse Life Than Damaged One?

I initially ordered the replacement battery kit for the iPhone 6 after leaving my phone in a car with the windows up at the beach.

My battery life was dropping off far too quickly after this, not surviving the night on standby. Upon installing the iFixit replacement battery, the battery life on the phone is even worse, dropping 20-30% over the course of two hours.

I suspect something is wrong with the phone itself as opposed the battery.

Has anyone else experienced such a steep drop-off in battery life with the iFixit replacement battery?