Spektrum SPM9548 - Manual (Page 7)

EN
External Voltage
External voltage telemetry is commonly used to monitor flight pack voltage or you can
monitor ignition batteries on gas engine equipped aircraft. You can set alarms in the DX8 to
prevent over-discharging batteries.
Installation
Plug the connector of the voltage sensor into the TEMP/VOLT port in the Telemetry
module.
Attach the opposite ends of the voltage sensor (stripped wires) to the voltage source you
wish to monitor. Note the polarity (Red = + positive /Black = - Negative).
Typically, you can solder the wires to the battery connector. At this point the external
voltage displays on the telemetry screen.
Note: A Y-harness is provided if you want to use temperature and voltage
sensors simultaneously.