iPhone 6 battery assembling

I have seen the mathod for replacing iPhone 6 battery

But as i see in video and photos we have to remove something down of battery

If I remove that thing as showen do i get problems to adjust new battery

Could u plz send me new video for assembling phone after changing battery

I want to change it myself

Coz I don't wanna show someone that my iPhone has a bad battery backup

I need to charge it 4 times a day

Sometimes it shows me 54% and suddenly it goes about to die

And switch off too

And again i start phone it shows me again 54% charged

So i wanna know that its a battery problem or not!!

I charge this phone with non apple charger

Can a duplicate charger ruin my battery?

Plz reply me respectively

A