Troubleshooting Unknown Battery Drain

If your battery drains after sitting a few days in your car, truck, motorcycle, tractor, camper or other fused circuit, the problem can be easily troubleshooted with below steps only using a multimeter.

Before testing, make sure you have a fully charged battery installed and there is no corrosion on your battery terminals causing an insulation barrier between the battery and the terminals. Corroded battery posts not only prevent the vehicle from providing electrical power or starting, but also prevents the battery taking charge from the alternator, external charger, or from jumper cables.

Parasitic current drain is the current consumption used when a device is off and should normally be pulling minimal to zero current. If the parasitic drain is higher than normal, it will drain the battery when the device is in its off state, which usually points to a defected component or circuit within the device.

  1. Key/power in off position
  2. Locate fuse box(es)
  3. Pull out a fuse
  4. In current setting, place multimeter leads across both terminals where the fuse was located to measure current. Most normal circuits should read somewhere between 0-100mA (zero or near zero is better). If you do not have an auto-ranging meter, you may want to set the meter in a slightly higher current rating than what the amperage listing on the fuse is when testing each fuse holder to prevent an internal multimeter fuse from popping. If the meter does not read any current in this setting, you can then slowly adjust the meter down to a lower Amperage or mA rating until you find the actual value of current being drawn, if any.
  5. Repeat this measurement technique across each fuse holder being used
  6. If current is more than 100mA in a given circuit, this will point you to what circuit is draining the power when key/power is off. If the circuit is reading above 300mA, this most likely is a problem but above 100mA is a good place to begin being concerned.
  7. Look at label inside fuse box cover, owners manual, or internet schematic to identify circuit function of the failing circuit and what sensor, module, or assembly can be replaced to fix the issue -if the part is too expensive or time consuming to replace, you can always simply leave the fuse unplugged for the parasitic problematic circuit when not in use to prevent battery drain, and plug the fuse back in when needed to operate.

See also:
Preventing and Treating Contact Oxidation
Chemicals, Cleaners
Electrical, Specialty Fuses
Test and Measurement Fuse Accessories
Rechargeable Batteries
Battery Chargers


dead battery after parked

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