Hi, I am about to add a Smarthunt 500A to my system. I understand how I need to connect it to the auxiliary battery and loads, but I would also like to monitor the starter battery with the aux connection, but according to the manual, I would need to put the negative behind the shunt (and the shunt …

The smartshunt can only monitor SOC for one battery (or bank). The aux input is used to monitor only voltage from a second battery. For this to work both negatives must be connected as is shown in your schematic.

In your case the starter battery and auxiliary battery probably are connected over ground/minus already. You could check this with a multimeter. Or, when you only connect the aux connection of the shunt to the auxilary battery’s positive, you should instantly see the auxiliary voltage in the app/VRM…

So, If I understand correctly, seeing that the aux only measures voltage of the starter anyway (and not current - which is good enough for me), it is not really essential to move the negative side of the starter behind the shunt? And knowing that the alternator charges both batteries with a simple …

[image] Franc: So, If I understand correctly, seeing that the aux only measures voltage of the starter anyway (and not current - which is good enough for me), it is not really essential to move the negative side of the starter behind the shunt? Correct. In fact doing so will make current bypa…

Alright, so I have been staring at the schematic and I realize 2 things… one of them makes me doubt mac’s answer (truly sorry, please correct me if I am wrong, I am not trying to be a smartass, just trying to understand): It should not matter on what side of the Shunt I ground the starter battery …

[image] Franc: It should not matter on what side of the Shunt I ground the starter battery as there is never a circuit with both batteries and Loads in it. If you 100% know what you’re doing and have a very good reason to, maybe, yes. [image] Franc: Chargers need to be behind the shunt i…

This FAQ answers how to connect the SmartShunt. [image] Shunt / battery monitor not reading the correct SOC/ Amps, missing solar, decreasing daily or other misreading problems DIY This topic covers the SOC / Amps reported by BMV battery monitors, SmartShunts, …

Thanks veryone for the clarification. One (final?) uncertainty is the circuit of my bow thruster. I am not entirely sure about the current it is drawing (it looks like there is a 280A fuse but hard to read), so would it be wise to put that current through the 500A smartshunt? You only use it in sh…

Some people have had the engine starter current going through the SmartShunt without any problems if they only have a single battery bank so a bow thruster should be OK.

Connecting the Smartshunt to both starter and auxiliary battery

DIY

pwfarnell 3 December 2025 19:49 8

This FAQ answers how to connect the SmartShunt.

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Connecting the Smartshunt to both starter and auxiliary battery

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