Hi Don. You size your shunt to handle the current you will be passing through it. Are you going to be using a dc to ac inverter to make 120v power? If so what size?

A 100 amp shunt would be plenty if you are only using 12v devices like water pump, furnace blower and lights. We have an inverter and pass up to 200 amps sometimes. The shunt that came with our monitor is good for 500 amps. It doesn't hurt to have a shunt larger than you need.

Typically the battery monitors include the shunt. Is there a model you are considering?

the 2004 bounder RV came with a 300 watt inverter, but I'm changing it out to a 1500. There is no transfer switch, It just turns on two outlets in the RV. But I want to install an extra plug off the inverter. Looking at the AiLi Battery Monitor Voltmeter Ammeter Voltage Current Meter 8-80V 0-100A . I do have the renogy bt-1 bluetooth module. But not wired to a shunt.
Thank you

100 amp would be too small. Which battery monitor are you considering? There are couple units that most end up with. The Trimetric by Bogart Engineering and the Victron. Ray has some videos installing the Trimetric if you haven't seen them. I believe that you order the shunt separately with the Trimetric. They offer a 100amp or 500amp shunt. Given the 1500 watt inverters capability to pull over 100 amps go with the 500 amp shunt. Victron includes a 500 amp shunt on their 700 series battery monitors.

Heres Rays video on the Trimetric.

https://www.youtube.com/watch?v=Q7OWOc7a0eA

Here is a link to the Victron for comparison.

Victron battery monitor

It looks like you added some more info to your post after I responded. I have seen a couple videos on the AiLi monitor. It appears to have the same function as the more expensive units. I am not familiar with the renogy BT1. Is it a battery monitor? The shunt should be located between the battery and all loads.

Here is a video review of the AiLi I see looking on amazon it can be ordered with a 350 amp shunt for not much more.

https://www.youtube.com/watch?v=E6O76Okmt08

thank you for the information

Don