Several things can cause Battery Drain issues. You will need to isolate some variables in order to get a better understanding of what is wrong. The problem could be a bad replacement battery, excessive current draw from on of the modular components (camera, button, screen) or it could be a problem on the logic board itself.
Here are some things to try:
- It could be a bad replacement battery; there are lots of cheap batteries on the market.
- Try replacing with a known-good battery or order a good one from here.
- You could have excessive current draw from one of the modular components; for example, the backlight, a camera or a sensor. You may notice a hot spot on the phone or screen.
- Fully charge the battery first.
- Disconnect the battery, then disconnect the flexes for the screen assembly, buttons and cameras, leaving only the Lightning Dock connected to the logic board (follow this guide). When you are done, re-connect the battery.
- Go back after an hour or more and test the condition of the battery. You will need to download either coconutBattery (Mac) or 3uTools (Windows) to see the battery condition.
- You may have a damaged logic board. This will require a micro-soldering repair and is not DIY. Drops, bends, water damage or using poor quality charging bricks and cables, can cause this.