....and gets very hot
That is not a typical symptom of a dying battery but is a common one when useless, third-party utilities are installed. Anti-virus, so-called "cleaning" apps, optimizers, tune-up apps, and client-side VPNs are all going to compete with components of the macOS and make the hardware work harder. Harder working hardware means extra heat and reduced battery run time.
Some browsers like Chrome can also run down a battery faster than others, as can leaving certain web pages open in the background (try amazon.com's home page, for example). So can using a extternal monitor.
Apple never sold replacement batteries for that model except to Apple Authorized Service Providers, so there are a lot of counterfeit batteries floating about. Most are miserable, even damaging.
On any Retina Macbook Pro, the battery is not user-serviceable. It is glued in place and requires toxic, flammable solvents and some force to remove. Many have created dead Macbook Pros trying to replace the battery at home. Service providers cannot use the solvent is a retail setting without violating a raft of HAZMAT and OSHA laws, not to mention fire codes. So batteries are a problem for older models that Apple no longer services.
So, if you have a load of fearware installed, it behooves to completely remove it and test before trying to rip out a battery the Apple did not design to be removed easily