Hi @ronaldjordaan
Fully charge the battery and then try using the phone in [https://www.hardreset.info/devices/samsung/samsung-galaxy-j4-2018/safe-mode/|safe mode] and check if the battery lasts longer.
If it does then a ''downloaded app'' may be the cause of the problem. The trick is to find out which one. You will need to uninstall each downloaded app, one by one and test the phone in normal mode to see if the problem is still there or not. If it works OK then the last downloaded app that was uninstalled was the culprit. A ''downloaded app'' is one that you downloaded and installed on the phone and wasn't pre- installed on the phone when you first got it.
If the battery still drains fast when using the phone in safe mode, then perhaps the battery is failing and needs to be replaced. Even rechargeable batteries have a lifespan.
Here's an image that shows how to remove/replace the battery in the phone.
Search online for ''Galaxy J4 battery'' to find battery suppliers that suit you best.
[image|3068490]
(click on image)