Auxiliary battery voltage

https://www.solar4rvs.com.au/victron-smart-shunt-300a-bluetooth-battery-monitor
If this is what you have, then you need another cable...
"Key Features of the SmartShunt 300A
The SmartShunt isn't just a battery monitor—it's a leap forward in battery system management. It's equipped with Bluetooth for wireless communication, a VE.Direct port for wired data transfer, and additional connections for monitoring a secondary battery or connecting a temperature sensor. Whether it's for midpoint monitoring or simply keeping your system's footprint small, the SmartShunt has you covered."
Cheers,
Peter
OKA196 motorhome

Thanks peter Shu05013005 300amp

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Hi Nick,

You say….. "measure the auxiliary battery voltage without any interference from main charging system or DC charger solar etc ."

Just be aware that it is not possible to accurately measure the battery voltage in any way whilst the battery is receiving charge from any source or while discharging to a load. Whilst any charging is taking place the terminal voltage of the battery will be elevated by a small amount. Furthermore, the only way to determine the "exact" battery voltage is to measure it at some time after it has been charging or discharging. The wait time can be about 15 minutes for a lithium battery and an hour or more for a lead-acid battery.

But it all depends what you mean by "exact". The error during charge or discharge can be as much as 1 or 2 volts and during the resting time following charge or discharge it may be half a volt or so.
Normally it is sufficient to observe the voltage soon after charge, say 5 minutes or so to obtain a reasonably accurate value. Otherwise wait an hour to see a more accurate indication..

Why are you interested in a very accurate reading?

Thank for reply ..sorry using wrong word :(
Dosen't need to be exact .

There are many other cheap and reasonably accurate other low cost ways to watch voltage on Ebay etc.
Voltage read-out
Cheers,
Peter
OKA196 motorhome

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Nick……
OK then, what Peter said goes.

But please be careful…. about "exhilary batteries". I got all exhilarated composing my reply. Now I feel 'flattened'. Doh.

@ Allan B - don't Start again - I dropped a Cell and suffered Attenuation after our last Connection.

Cheers
Greg

OK Greg, I'll pull the plug.

Thanks peter , few good video's on this subject. Have been looking for info on setting for ledacid battery . Cheers