Cheap Battery monitor.

[Cuppa]

My aux battery is earthed to the chassis and also has a direct earth to the start battery, with this shunt on the negative side would it simply display the complete vehicle battery (ie. both batteries) capacity?

I also have 6 B&S twin core going from the aux batt to the rear of the vehicle to a distribution fuse block and earthed to my rear drawers with a stud for easy earthing of rear accessories. I'm just trying to get my head around where the best spot for the shunt would be, and if it actually makes a difference to what it reads/sees in terms of amps etc.

If I put the shunt inline with the 6 B&S negative, it would be pointless having a higher amp shunt than the capacity of the cable?
Or do you simply place the shunt in the biggest negative cable attached to the battery, such as chassis earth cable?

Firstly, this is testing my level of understanding so don’t take what I say as 100% gospel.
Secondly without seeing a wiring diagram of your setup giving answers to your question is difficult for me. Others more knowledgeable may be clearer.

However:
I think that if all the negatives to aux battery are connected to one side of the shunt , with the other side of the shunt connected to the Aux battery neg terminal, then the battery monitor could function fully (ie. show real time voltage, amps in & amps out, plus State of Charge % for just the aux battery. This assumes that you have nothing which draws current from directly both batteries. (i.e. a positive cable to the same accessory from both batteries - highly unlikely).

In terms of what amperage monitor to get....... it should be enough to cover the combined amperage of everything that is powered off the aux battery which could be used at the same time. Thus you need to know the max current draw of each accessory.

If anyone can confirm or correct what I’ve said I’d appreciate it.