The easiest way is just replacing the uppercase assembly as replacing the panel alone is quite hard. This is the bare part MacBook Pro 15" Retina (Mid 2018-2019) Upper Case and here's the version with the battery MacBook Pro 15" Retina (Mid 2018-2019) Upper Case Assembly
Install this gem of an App to check your batteries heath CoconutBattery take a snapshot of the Apps main window posting it here so we can see it too.
To help you see the cost of adding a fresh battery alone MacBook Pro Battery. Reusing batteries is risky! Li Ion batteries are setup as two plates with an electrolytic between rolled up in a sizable with about 75 layers. The gap between the plates must stay at a distance otherwise the battery shorts out which creates a runaway thermal event sending the system a hot mess! This series is not easy to pull the battery without hurting the battery.
Sorry we don't have a guide for this series to replace the TouchBar or the upper case. We do have a guide to replace the battery which is more common a task MacBook Pro 15" Touch Bar 2018 Battery Replacement. Take a look at the other series guides to get an idea on what's needed.
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