BC300 + CommLink

300A External Shunt


  • High current/external charge  monitoring
  • Wireless Bluetooth communication to Commlink – easy to install / retrofit
  • DIY installation and simple pairing procedure
  • Compatible with Lead Acid and LiFePO4 deep cycle batteries

Battery properties monitored:

  • Voltage
  • Current (charging / discharging)
  • Energy usage (Ah)
  • Temperature (not displayed)


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Why you need a BC300

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How To Install BC300

Monitor all connections direct to battery

The BMPRO BC300 External Shunt and CommLink provides additional battery monitoring for your BatteryPlus35 and J35 battery management systems, connecting directly to battery via the BC300 External Shunt. This enhances system behaviour with temperature monitoring of the battery for greater protection.

The addition of the BC300 to the BatteryPlus35 and J35 battery management systems allows high current loads and external charge sources.

The BC300  also provides your BatteryPlus35 and J35 with additional information on battery usage so your displays such as the Trek, JControl and JHub are always up-to-date on battery Time Remaining and State of Charge.

The BC300 External Shunt and CommLink communicates via Bluetooth and CAN bus. The BC300 External Shunt is designed for 12V batteries up to 800AH in capacity. The shunt is rated for ±240A constant and 300A peak.

What our customers say:

We love our BC300 with CommLink. We both use CPAP machines and my wife uses a small hairdryer, so knowing where we sit with battery capacity, lid and charge rates is great. All reported on the JControl panel. Thanks BMPRO.

– Mark Simpson,Umina Beach, NSW

Product Specifications

Voltage Range 8V to 16V
Current Range +/-300A
Capacity range 7-800 Ah
Compatible Battery Types Lead Acid, LiFePO4
Compatible BMPRO products BP35 series, BP35-II series, J35 series, Control Node and Odyssey Link series, Trek series, JControl, Odyssey, JHub, phone apps JHub and Odyssey
Dimensions 140mm x 65mm x 18.6mm
Weight 520g


A BC300 is required for any load or separate charge source going directly to the battery.                                

Below is a list of items that are fitted directly to batteries in caravans:                                     

 Inverters (of any size), diesel or gas heaters, air compressors, portable solar panel, DC/DC chargers (in any brand), additional fridges, Wi-F, satellite TVs, additional high amp 12v plugs (Anderson plugs, 50amp, 80amp, 100amp, 150amp), additional lighting, electric steps, slideouts, electric water pumps electric jacks, winches.           

The BC300 is not hard to install. You will need to disconnect the battery. There are instructions on how to disconnect the battery in your BP35/J35 user manual.                                           

Once the battery is disconnected, the installation is very straight forward. Follow the instructions in your BC300 user manual.       

The BC300 does not have its own app. The BatteryCheck range and the BC300 are two different products for two different applications.

The BatteryCheck was designed as a stand-alone app as a wireless battery monitor, while the BC300 was designed as an addition to use with the BP35 and J35 range of battery management systems to allow excessive loads from the battery to be monitored through your caravan’s digital display.

Both units can communicate to each other 25 meters away from one another in open sight.

The BC300 and CommLink lights will always flash green when paired.      

On the CommLink unit, there are two CAN bus ports. The BC300 kit comes with a small CAN bus lead. Simply unplug the CAN bus from the right hand side of the BP35. This lead can be plugged into the CommLink.                                 

The spare port on the CommLink can now have the small lead that was supplied in the kit plugged in. The other end of the small lead can be plugged back into the BP35.                  

On the CommLink unit, there are two CAN bus ports. The BC300 kit comes with a small CAN bus lead. Simply unplug the CAN bus from the bottom-left hand fromt side of the J35. This lead can be plugged into the CommLink.           

The spare port on the CommLink can now have the small lead that was supplied in the kit plugged in. The other end of the small lead can be plugged back into the J35.      

Consider the following:                                 

How much current is the caravan using compared to the current available from the J35/BP35 to power loads and charge the battery?

If the caravan is using most of the available current to power the loads, there will be less current available for charging. This means it will take longer to charge the battery and the state of charge graph won’t fill as quickly.   For example, if the J35/BP35 is powered from the solar input, and solar is providing 6A of current, but the caravan accessories are drawing 5A of current, then there is only 1A of current available to charge the battery.   

Is there a charge source fitted directly to the battery?

The J35/BP35 can’t see current flow at the battery if an accessory, such as generator, is connected directly to the battery. If the J35/BP35 doesn’t see the current, neither does your battery monitor.                                

 If you are planning on connecting any load directly to the battery, you should install BMPRO’s BC300 External Shunt + CommLink. The BC300 allows the J35/BP35 and monitor to see the current flow from sources connected directly to the battery, so you are always correctly informed on the power into and out of your battery.

Portable solar will not show up as a source on your display. Instead, it will show as a total of the amps going to the battery when charging, as the BC300 cannot determine where the charge source is coming from. The BC300 can only show charging and the total amperage going to the battery.        

If your battery management system has an inbuilt solar regulator, unregulated solar panels should connect directly into the J35/BP35 solar input terminals. There is no need to install an external regulator between the solar panel and the J35/BP35.                                    

If you want to add an additional regulated solar panel or a blanket panel, it needs to go directly to the battery, and would require a BC300 fitted so that your battery monitor (JHub, Odyssey, Trek, RVView, JControl) reads correctly with the coulomb counting.                                        

If your J35/BP35 is not solar compatible (J35A and some earlier versions of the J35B, BatteryPlus35-PM), you can install your solar panel directly to the battery through an external regulator. If you want your battery monitor to see the solar charging current at the battery, you will need to also connect the negative through the BC300 shunt.