Battery Shunts Explained

Shunt’s (battery monitors): “What are they?”, and “What do they do?”, and “Do I need one?”.

A Victron battery monitor

What is a Battery Shunt?

Simply put they are a fuel gauge for your battery bank, and the only way to know accurately where your battery bank is at.

You wouldn’t drive a vehicle without a fuel gauge but most operate the most expensive replaceable part of the RV (the batteries) without one.

So a shunt is very similar to the power meter on a house wall that measures all the energy going in and out of the house so the power company knows how much to charge you and or credit you if you have solar at home.

What does a Battery Shunt do?

A shunt is very similar to the power meter on a house wall that measures all the energy going in and out of the house so the power company knows how much to charge you and or credit you if you have solar at home.

The shunt is placed next to the battery bank and connected to the negative of the bank and measures all the consumption and all the charging to tell you the SoC (state of charge) of the battery (how full is the battery bank).

Anyone struggling with what is SoC, most of us have cell phones, they all display a percentage – that is the SoC.

My phone says 71% at the moment so I know from experience I don’t need to worry about recharging until tonight, it’s as simple as that. The shunt let’s you make informed decisions about your energy use.

Who Should Use a Battery Shunt?

Personally I think every RV that is used off grid should have one. The more energy your system uses the more critical it is to know where the batteries are at, most understand that inverters use more than most standard DC systems, so if you have an inverter you should have a shunt!

To put usage into perspective below is a list of appliances that are big users of energy and can compromise batteries very quickly if the system is not set up/managed for the load.

  • Hair dryers
  • Hair straighteners
  • Jugs
  • Toasters
  • Coffee machines
  • E bike charging
  • Air fryer
  • Crock pot’s to name a few

The cost of a quality shunt starts at around $200 to $250.

“A couple of myths to dispel, there are some solar controllers that show images of batteries and how full they are, these are not accurate!!”

The images of a battery’s charge can on occasion be accurate, but not the way we use energy in RV’s.

It is virtually impossible to tell the SoC of the batteries from voltage alone. As an example a voltage of 13.5 could indicate your battery is low but charging, or it could indicate that the batteries are full and in float.