2017 Macbook Won’t turn on – Displays battery icon

The fact that your computer shuts down at 50% remaining charge and also that your MagSafe LED remains orange makes me think that either the replacement battery isn't an official Apple part, that it is defective/DOA, or that your logic boards SMC is corrupted and needs to be reset.

If the battery is indeed new and Apple original than proceed with an SMC reset:

http://support.apple.com/kb/ht3964

This will tell the SMC chip to reset all power states and reboot so that it forgets the battery and MagSafe adapter momentarily and then rediscovers them.

Hope that helps

Because you explain the problem perfectly, and in short:

• The battery does not charge, and your Macbook does only work with MagSafe attached

There's only one option what could be the problem...

The battery is dead, let me explain you why:

1. Your battery is ignored somehow, and your Macbook uses power directly from the MagSafe adapter. If you couldn't even use the Macbook with the cable in it, the cable could be the problem. Since it works with cable-attached, it's not.
2. You can use the macbook with cable in it as explained above.