slow on battery but fast on charger

Hi everyone

I've got very unusual problem with my MacBook (bought on Gumtree)

It is slow when just on battery - but it is fast when charger connected (just I have to reset it with SMC reset to be fast again)

It had non-genuine Apple battery in it - then I've bought 2 other non-Apple batteries (everyone different brand) and designated to my MacBook Pro 15" 2011 model (and they hold charge as they should)

Been at Apple Store - they said - everything is fine - and they can take it for extended diagnostics - but if non-genuine Apple battery in it - they cannot touch it (replace it to genuine Apple)

And now funny part - I've "fixed" that problem with deleting that file:

sh-3.2# cd /System/Library/Extensions/IOPlatformPluginFamily.kext/

sh-3.2# cd Contents/PlugIns/ACPI_SMC_PlatformPlugin.kext/

sh-3.2# cd Contents/Resources/

sh-3.2# ls | wc -l

sh-3.2# mv MacBooPro8_2.plist /Users/

But I wish to have all fixed as it should (especially if I'm not sure if after update do macOS Sierra it will be slow again) - basically cannot believe 3 different batteries (sadly non-genuine Apple) what those shops sell do not work with MacBook as they should

Obviously I could buy genuine Apple battery but I do not want to risk loosing another £50 "just to check"

What could I do to be 100% sure what is wrong?