Starter motor Audi q7 08

[Jjgoldey]

So my Audi was a slow starter diagnosed slow starter motor was a pig to start something then would pop up low voltage. 
so change starter motor with a cheap ishhh one started spot on. Well for 2 days then I had nothing at starter so thought buy cheap buy twice so ordered a Bosch put that it stil nothing g battery’s is new and fully charged all light on what you people think it can be. 

[Magnet]

Hello John,

Thanks for joining.

Worth a forum search - wasn’t there something about poor engine earths, and adding another earth-? 
Kind regards,

Gareth.