Parasitic loads

In more and more applications the phenomenon of parasitic loads is showing its ugly
Ihead. So, what are parasitic loads? Parasitic loads are small currents, typically with a
magnitude of a few milliamperes (mA), that the battery continuously delivers for various reasons.

Holding up memories and operating security systems are common examples of parasitic drains on batteries.

Even though the current drains are low, their impact on a long-term basis can be significant when the battery has to provide the drain for weeks or even months at a time. An example will make this clear.

In some models of Sea-Doo personal watercraft the drain on the battery, with the engine
switched off and the battery connected, varies from 7mA to 18mA, depending on whether or not the lanyard is installed. If the watercraft were equipped with a PC 625, it would take 95 days to be fully discharged at the 7mA rate; at the 18mA rate it will lose 100% of its capacity in only 37 days. Since the PC 625 needs to have at least 30% of its capacity to crank the engine, the maximum number of days that a parasitic load can be tolerated is less than the numbers given above. Table II below shows the number of days needed to reduce the battery’s state of charge (SOC) to 0% and 30% with an 18mA parasitic load. Should the parasitic load on your vehicle be some value other than 18mA, prorate the number of days given in Table II. If, for example, the load is 10mA, multiply all days in the table by the fraction 10/18 or 0.56. This table assumes that the ODYSSEY battery is fully charged when placed on storage.

Table II: Effect of an 18mA parasitic load on storage of ODYSSEY batteries

  PC 535 PC 545 PC 625 PC 680 PC 925 PC 1200 PC 1700
Days to 0% SOC 32 30 37 37 60 97 162
Days to 30% SOC 22 21 26 26 42 68 113

Table II shows how critically important it is to make sure that your battery is not being
drained by a parasitic load; if it is being slowly drained, the battery must be connected to a float (trickle) charger that will help compensate such capacity losses. Alternatively, physically disconnect one of the battery cables to interrupt the small drain.