question

Generally speaking, shunts should only be run at 60-80% of rated current continuously depending on manufacturer. However, they are also very tolerant of brief overloads.

What it comes down to is heat. The shunt is actually a precise resistor across which the voltage drop yields current. Heat will alter the readings, AND excessive heat can permanently change the accuracy of the shunt.

The downside to a high current shunt relative to your normal loads is that you lose resolution at lower currents. On a 500A shunt, each 1mV drop across the shunt is 10A. In a 1000A shunt, it's 20A... 2000A shunt, 40A.

What really matters is the actual current you'll be drawing. If you're really going to pull >1000A , but likely less than 1500A for a few seconds, I would think a 1000A is okay, but I can't back that up with facts specific to the smartshunt.

Thank you, that's very helpful. I'm a little unclear on what you mean by losing resolution at lower currents. What is the practical implication of that? If I'm following the math, a 10 amp draw on a 2000A shunt would equate to a .25mV drop, and a 1 amp draw .025mV. Does the drop become so negligible that is can't be read?

Have a look at this thread

https://community.victronenergy.com/questions/284103/bmv-712-on-starter-battery.html?childToView=284338#comment-284338