Battery not detected after replacement on Macbook Pro 2017

Closely inspect the battery cable to see if there are any rips or tears.

If the battery cable is removable, then make sure both ends are fully seated and latched into place. The latching levers for those connectors are very fragile & easily broken so make sure both latching levers are locked down.

Also, you did remember to reinstall the T5 Battery BMU screw (the one with the large screw head)?

While iFixIt and OWC are both respected vendors, even their batteries can be bad, or perhaps the battery or Logic Board were damaged during installation (I'm assuming you did not have this issue with the original battery).

Just to confirm: The battery icon is present and shows the battery has a charge on it? And the battery can power the laptop?

Try connecting the power adapter to another USB-C port especially on the other side of the laptop.

Try disconnecting the power adapter from the electrical outlet for a minute in order to reset the power adapter.

Try an SMC Reset.

If there is no battery seen by macOS, then one or more of the following is causing the problem:

• Issue with the battery cable or connector(s)
• Defective battery
• Accidentally damaged battery
• Accidentally damaged the Logic Board (most likely the battery connector on the Logic Board), but could be some other component has been damaged on the board.

Connect the power adapter and charge overnight. it will likely only trickle-charge in that time.

In the morning, reset the SMC.

Then see if the battery is recognized.

Once recognized, continue to charge until reasonably full.

Always connect to AC power when available, your Mac will NEVER over-charge.