There's some questionable mods done to the battery lead end there. If you have a multimeter, try putting the truck battery on charge for a while then attempt an engine start. Check voltage across the battery. If it's not climbing or making more than 13v, something is up with it. Also do the standard battery health check (hydrometer + acid level visual check) It takes a bit of current to get the starter motor cranking so if the charging system is struggling, so too will the starter motor.