The Mac Pro (big, expensive desktop workstation) does not rely on battery power. It is designed to run only on wall power.
A Mac Pro has a tiny backup battery to maintain settings when the computer disconnected from wall power for service or moving. However, the computer will start with that battery dead or missing.
Perhaps do you have a MacBook Pro laptop instead? People struggle with Apple's too-similar model names all the time. If you have the laptop, we can ask the moderation team to move you to a more active and appropriate forum section. This section get few views so help will be slow in coming.