If you’re reliant on your vehicle to work, one of the most frustrating events that can happen is your engine not starting when you need it to. You could have sworn that everything was checked out, that your battery was still pretty new, that it hasn’t been that cold outside lately…so what’s going on? Well, you might be experiencing a phenomenon known as parasitic power draw.
 
What this means is not that your battery is the problem. In fact, your battery is likely perfectly fine! Instead, it’s the vehicle’s electrical system – all the chips, clocks, monitors, and other components that take power from the battery – that has an error somewhere that is keeping the circuit open, and pulling power from the battery when it shouldn’t be. This results in a loss of power, and ultimately the inability of your starting apparatus to turn the engine over. If you just got a new battery and you’re experiencing this problem, now you know where to start looking for the trouble!
 
If your old battery was “bad” and drained of power, don’t rush in to buying a new one just yet – because if phantom power draw is your problem, you’ll just have the same issue with a new one, and you’ll drain your pockets too. Before replacing the battery, bring your vehicle in to West Tech Mobile and let our mechanics double-check all the electronics to identify the true problem.
 
Our techs will fully recharge the battery, and use what’s known as a battery cranking amps test, to see if it is capable of putting out enough power to start the engine. For example, a battery might be rated for 1000 cranking amps, so if it is tested and only has 700, that might be the problem. Of course, this is all dependent on the age and condition of the battery, among other things, but in any case, a battery that is less than two years old should still work well.
 
So how to check for parasitic power draw? This is a good trick to be able to do on your own before you buy a new battery, because you can discern whether the battery is the problem, or a faulty circuit. You’ll need some basic tools, as well as a multimeter, and you’ll have to be familiar enough with your vehicle to know where the fuse box is.

1. Disconnect the battery’s negative (black) terminal.
2. Connect the multimeter, with a fuse larger than 10 amps, between the terminal and the cable that you previously disconnected. Check the amperage draw; it shouldn’t be higher than 50 milliamps (mA).
3. If the draw is less than 50 mA, you do not have parasitic power draw. If it’s more than 50 mA, you’ll need to discover which circuit is pulling the extra power from your battery.
4. One by one, remove the fuses from the engine compartment, referring back to the multimeter amp draw reading. When you see the drawn current drop after removing a fuse, you’ve found the circuit containing your parasitic power draw!
5. Identify all the switches on the circuit and make sure they work properly. (WARNING: when checking switches or opening doors, disconnect the multimeter from the battery, or you will blow the fuse inside it!) It may be something as small as the light in the glove box that stays on when it shouldn’t. If all the switches work correctly, the problem is more complex.
6. If you’ve reached this point and still cannot find the exact source of the power issue, it’s time to call in a pro. The problem is most likely in the vehicle’s harness, engine computer, or other complicated systems, and trying to disassemble these yourself will probably end in a bigger mess. Trained technicians, like the ones here at West Tech Mobile, will be able to reference electrical diagrams to pinpoint where the trouble is.
7. If you were able to successfully locate and fix the problem, reconnect the multimeter and check to make sure the battery draw is less than 50 mA.

 
 
If you’re not sure you want to dig under the hood of your vehicle, or you don’t have time to do the whole process on your own – we’re more than happy to help get to the root of your parasitic power draw. Wherever you are in Calgary, Alberta, or the surrounding area, our fleet of mobile technicians can come to you to get you back on the road. At West Tech Mobile, it’s what we’re best at!