I measured it with a brand new multimeter.
It's actually this car booster I'm talking about : https://www.amazon.com/UTRAI-Jumpstarter1-Portable-22000mAh-Cigarette/dp/B07WVCRQPC/ref=sr_1_1_sspa?dchild=1&keywords=UTRAI+Booster+Batterie&qid=1611494816&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExN0pBSFpQSFZRRDNPJmVuY3J5cHRlZElkPUEwODIzMDQ1MVpIUzNFN0tDUDFJUiZlbmNyeXB0ZWRBZElkPUEwMzUzNTUyMloyNkVDOTlJT0Q3WiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
Also comes with a cigarette lighter socket (12V-17V/8A-10A) can power your toy car,telescope or camera,etc
Thanks for the advice, this is what I should do then