Concorde Battery Corp. recently issued Technical Bulletin No. 10 “Parasitic Drain” in response to questions throughout the aviation community about the effect of parasitic drain on battery state of charge. A parasitic drain is an electrical load that takes power from the battery even when the Master Switch or Battery Switch is Off. Examples of loads that cause parasitic drain include clocks, lights, relays, current sensors and power monitoring circuits.
If an aircraft is inactive for a length of time, depending on the magnitude of the load, the battery may be depleted within weeks or even days. Skip Koss, vice president of marketing says, “When an aircraft is not in service, a parasitic drain will deplete the battery’s state of charge unless the drain is disconnected. I am concerned about the increasing number of aircraft affected by parasitic drain, which can diminish emergency capacity reserves and compromise the safety of pilots and passengers.”
Parasitic loads are present in most modern day aircraft. They are generally low in amperage but because they are continuously present, if an aircraft is inactive for an extended period of time, they can deplete the battery’s capacity and cause the plates to sulfate. Sulfated plates make the battery harder to recharge and over time can lead to a battery that is no longer airworthy and, ultimately, premature failure. One of the inherent dangers is that a battery without enough emergency power reserve can often still start the engine(s). A battery that is no longer airworthy can also cause an AOG event with unexpected expenditures for obtaining an urgent replacement, freight, installation and possibly costs for transportation back and forth to a hotel for overnight accommodations.
To preserve the life of your battery, Concorde recommends measuring the parasitic drain, which can be easily accomplished using a standard digital multimeter (DMM) equipped with both 10 Amp and milliampere jacks for test leads. Details for this procedure and a formula to calculate the depletion rate can be found in Technical Bulletin No. 10 “Parasitic Drain” on the Literature, Manuals and Technical page of the company’s website. In some aircraft, modifications can be made to reduce or eliminate the parasitic drain however, the airframe manufacturer should be contacted for information on this subject, company officials note, adding the best practice to protect an inactive aircraft battery from parasitic drain is to disconnect it, if possible.