It is just an alternator that can supply more amperage than the factory alternator . Car manufactures have to keep production costs low so they only install alternators with enough to run what the car comes with and a bit of extra headroom . For lower power systems like 7501250 watts stock alternators are usually fine but higher power systems usually require an upgrade . <| sep |> Please note that this isn ' t the case in all statescountries . Some of them where I live , for example don ' t allow emergency calls without a SIM card , to prevent a large number of fake , untraceable calls . It is worth to check and confirm . <| sep |> Downvoters with a serious case of shit memory . Recall , if you will , the jagoff Boston fan who said this kind of shit a million times over in rhockey . There was plenty of chatter about it in our sub . Did this REALLY need a s ? For fuck ' s sake , people .