I know you said boss but then you said your battery was dead. If its company truck and battery was dead meaning they sent someone out to jump it. I dont knw why they would even be tripping.
Unless of course the time in which you called in for dead battery was so late that you wouldnt have made it on time anyway.
Still i dont see how they could charge you. Even though they might have gotten charged from receiving company.
If its your truck, dont knw why you're saying boss. Are you leasing. In either case if you own truck or are leasing then you may have autborized them to charge you in paperwork that you signed.
Companies are going to get more strict on making appointment time due to ELDs. But its going to go both ways. So it will also eventually mean less waiting at the dock.
So be sure to get ready to leave to appointments early and check out truck. Even you cant leave but so early because it starts your clock.