The Yellow bar is your charged capacity, it is based on your charger ability to charge as well as how long you let it charge.
I would replace the charger with the proper one as their are a lot of knockoffs which don’t work properly and I would also inspect the MagSafe connector on your system is the contacts clean as well as the plastic area [https://www.apple.com/shop/product/MD506LL/A/apple-85w-magsafe-2-power-adapter-for-macbook-pro-with-retina-display?|Apple 85W MagSafe 2 Power Adapter (for MacBook Pro with Retina display)]
Why you don’t want a Knockoff charger!
* [https://lifehacker.com/dont-replace-your-macbook-charger-with-a-cheap-knockoff-1825605569|Don't Replace Your MacBook Charger With a Cheap Knockoff]
* [https://beetstech.com/blog/oem-magsafe-chargers-vs-counterfeits-teardown-for-truth|OEM MagSafe Chargers vs Cheap Imposters: Teardown for Truth]
* [http://www.righto.com/2016/09/why-you-shouldnt-use-cheap-macbook.html|Lacking safety features, cheap MacBook chargers create big sparks]
* [https://www.youtube.com/watch?v=DrxAuhrrLU4|FAKE Magsafe MacBook Chargers on eBay - Watch before buying a Mac Charger]
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