I put new starter relay n new starter n selenoid n alternator n Wont hold charge

so I did put a multitester on alternator n it said charge was fine so why vechile wont start or keep its charge is to tAke battery out n charge it to a battery charger if alternator is charging correctly when u put a multitester on alternator n replaced everything else as i said early so it could b battery needs to b charged as it went below 8 on the battery gauge on dash ant mechanically overly smart I am was TLD battery charges when another vechile n mine has cables on them but UR saying take battery out n hook it up to a booster PAC to charge battery! TKS in advance

i think you have more than a battery problem! charge the battery until fully charged with a battery charger.and NO,you can not charge a dead/fully discharged battery with jumper cables from another vehicle. 8 volts is discharged and/or a dead short maybe? take the battery and the alternator to Autozone..they will try and charge your battery and test your alternator for free! if the battery takes a charge and the alternator test good and you put them back on your truck and the volt meter on your dash drops to 8 volts again,then you have a dead short on your truck somewhere! a fully charged battery is 12.6 volts with the engine off,,when you start the truck and check the battery voltage again on the battery terminals with the engine running,the volt meter should read 13.0-15.0 volts! this is your alternator output...