freightliner jump starting question

Are they smoking with key off, or when you attempted to start?

 

With main power on, key off and vehicle on low idle

 

Reasons I know of why a battery would be smoking.
1) alternator overcharging.
2) battery plate internally is shorting.
3) loose battery cable/connection, the wire vibrates at the connection and arcs, essentially acting like a welding arc.
4) battery cable or connection shorting. Insulation worn off or under a cable clamp worn to the copper wire.

If you smell rotten eggs, Turn your truck off, let the batteries vent with fresh air. (That gas could be explosive.) Disconnect all your batteries from the cables.
If the batteries smoke with the truck turned off. Key off. The battery has a plate shorting inside. Get rid of that battery.

Load test your batteries individually,
Wear safety glasses when you work with the batteries.

Good luck

 

Thank you very much. Off to pull and buy two new batteries. The that was smoking with the key off and the one next to it.
Actually now that im thinking about it. Im just gona change all four under the cab and get the other four load tested soon