You’ll need to visit an Apple Store or authorized service center to see if you can get them to fix your system under warranty. I fear the battery has failed due to lack of use.
Li-Ion batteries are tricky! They can sustain a charge as long periods of time as long as there is no drain on them.
Apple uses a constant drain design for the Touch-ID to work. So storing the system for long periods will exhaust the battery to a point it can’t be workable.
Getting to the discreet cells to manually charging the cell with the proper Li-Ion charger is just not practical or safe. The problem here is the battery is sealed so you would need to take the battery fully apart to the point you can’t use it in your system.
Your only hope is replacing the battery, If you can’t get it done via Apple under warranty, you’ll need to find an independent who can do it but they will charge you the price of the battery and labor.
Here’s the needed part [https://www.thebookyard.com/product.php?cPath=39_367_616&products_id=21842|13” MacBook Pro - Battery (18/19) Apple P/N 020-02497 (Used)] and here’s the proper process [guide|124522] You need the battery I’ve given you as the 16/17 model uses a different cell configuration.