Do I NEED to use a Battery Support Unit (BSU) when programming to a ECU? 

Brendan Randle You could but this doesn't solve the draw on the battery on for instance a 2009 Range Rover with air suspension that power down the air compressor and all the ECUs on the car to which there is many. All these ECUs create a big draw of power on the battery and a battery support unit is still needed even if the radiator fans was disconnected I hope this helps! Lewis

When the cars computer is programmed the fan comes on as a fail safe as while the ECU is being programmed it doesn't know if the engine is hot or cold so it cools it to be on the safe side

Split charge relay, inverter and leisure battery

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