JP1 enables/ disables the reverse input voltage protection diode. Leaving it removed has the diode connected in series with Vin, protecting against reverse input voltages, but adds an extra 0.4V drop at the input. For long term battery powered applications, it should be disabled (jumper fitted).
JUMPER IN = NO REVERSE VOLTAGE PROTECTION
JUMPER OUT = REVERSE VOLTAGE PROTECTION
Please Note: The Flexi 1 is not an automotive spec device. Even with the reverse input voltage protection enabled, to ensure low power usage, there is no input protection. Care must be taken when supplying power to the device.