MacBook Pro Charging – How to Know if MacBook is Charging While Turned Off

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

Reset the SMC.

From https://support.apple.com/en-us/HT201295:

On Mac notebooks with non-removable battery Mac notebook computers that have a battery you should not remove include: MacBook Pro (Early 2009) and later, all models of MacBook Air, MacBook (Late 2009), and MacBook (Retina, 12-inch, Early 2015). To reset the SMC: Shut down the computer. Plug in the MagSafe or USB-C power adapter to a power source and to your computer. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. Release all the keys and the power button at the same time. Press the power button to turn on the computer. On MagSafe power adapters, the LED might change states or temporarily turn off when you reset the SMC.