On 23.04.17 19:44, wrote:
I have zero knowledge of shunts. Maybe this evening.

I see the recommendation has company:

https://powerwerx.com/blue-sea-1732-...nel-dc-ammeter

rated at 100 amp shunt. If I add an external 100 amp shunt to the internal shunt what does the meter read ?

what is a shunt doing to the flow of electricity back to charging the battery ?

why should you add a second resistor?
Just read the voltage across the the one already there.
You cannot disturb anything by adding your voltage meter to it.