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ford-donald suggested

Using a Cerbo GX relay to manage heated batteries

I have configured Cerbo GX to manage the internal heating of lithium batteries based on external temperature sensing and a relay. I haven't seen any other posts of this nature so I thought I'd write up the solution I found.

The Need: The enable the internal battery heaters built into Battleborn lithium batteries automatically, and only as long as needed, to allow charging, based on temperature sensing.

The Environment: A travel trailer stored outside in low ambient temperatures. Trailer has heating-equipped lithium batteries, solar charging, an inverter to channel shore power charging and related DC + AC loads in the trailer.

The Solution: I wanted a way to run the internal heaters inside the batteries only as much as needed to keep the battery temp high enough to accept charging. The heating function of the batteries is enabled by simply putting 12v on a sensing terminal at the top of the battery (each). The manufacturer's solution to this is to include some jumper wires and a SPST switch. The downside to the solution is the internal heaters consume a good deal of energy, enough to drain a commonly available 100Ah battery in a matter of a few days. The way to automate this to use it only just as much as needed is to combine the Cerbo GX's temp sensor input with the dry contact relay to make & break the enable 12v signal as needed.

To configure this, you need a temp sensor either wired to the Cerbo GX (such as the one included with a Multiplus Inverter), a bluetooth one such as a Ruuvi or other compatible temp sensing source. Ideally, place this temp sensor on the battery negative terminal or immediatly adjacent to the battery bank. Enable the sensor in the Cerbo GX UI. (here, showing wired input 1)


Then, choose one of the two relay connections on the Cerbo GX and wire a 12v source (from the battery + terminal, or anywhere you can get a reliable 12v tap) to the COMMON (center) port so your relay has a 12v signal to use when needed. The run a wire (small gauge 18 AWG is fine) from the relay's NO (normally open) contact to the trigger post on the (or the first) battery. Daisy chain the other heater trigger posts as per the Battleborn instructions so all the batteries get the same signal at the same time.

Configure your chosen relay in the Cerbo GX UI to be temperature triggered. This enables the ability to set temperature rules in the UI once enabled.


Now you have a relay opening and closing the 12v signal connection to the trigger terminals on all the batteries based on rules (here, showing ON at 28 degrees F and OFF at 34 degrees F) based on the sensed temperature of the battery itself.

The result should look something like this, where the temp holds steady between the lowest allowed and the highest programmed in the temp rules, as long as the ambient temp is lower than both of these. The battery heaters only operate as long as it takes to warm them to the preset deactivation value, then are off. If the ambient temp warms up, the relay stays open (Off) indefinitely with no power used inside the batteries to heat them.


cerbo gxTemperature SensorRelay
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1 Comment

oldchubbyknuckle avatar image
oldchubbyknuckle commented

Excellent! Thanks for taking the time to document this so well!

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