19 Mar

Detecting Battery Drain Issue on All Vehicles

Post Credit Kenzo

Here’s a quick step by step breakdown on how to detect battery drain on your vehicle for any vehicle type.

Ever woken up to a car that won’t start, especially if you last used the car less than a week before? Or walked down to the car park after an event and your car just didn’t start?

The first way to know if the batteries are the reason the car won’t start is if the engine rolls weakly or the dashboard lights dim when you turn the keys, but the engine crank doesn’t even roll. Now if this problem happens quite frequently, say 2 to 3 times in a month, or consistently over a shortening time interval, then there is likely to be some electrical component draining the car battery.

Some mechanics will tell you to leave your car with them for a week. They remove a suspicious fuse to see if the battery is drained by the next day. If yes, then the suspected fuse is guilty. If no, then the process is repeated with another suspected fuse until the culprit is found. QUITE A WASTE OF TIME!!!

A way to instantaneously detect the drain is simple. You will need a multimeter that can read up to 20A. It is a simple tool that can be found in any electronics store. Many electrical technicians own one. 2 major ways to check are by voltage and by current.

1. Testing voltage drop and the alternator. Set the multimeter to read voltage of up to 20V. Put one wire from the multimeter on the negative terminal of the battery and the other on the positive. It really doesn’t matter which wire to which terminal for voltage measurement. If the car is on, the multimeter should read at least 13V. 14V is healthier. This shows that your alternator is charging your battery which is normally around 12V. Any reading below 12V while the car is on indicates a bad/weak alternator. When the car is witched off, the reading drops to about 12 – 13V and stabilizes somewhere in between. If the voltage keeps dropping (and quickly too), then there is a fuse draining the battery and it is quite bad because voltage drop shouldn’t be very quickly detected unless they are really severe.

2. Testing current drop. Current drop measurement is more sensitive than voltage so you can see the drain immediately. On the multimeter, connect the black wire to the com input and the red wire to the 10A or 20A input on the multimeter. The meter needs to be able to read at least 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won’t work and could damage the meter. Then disconnect the negative wire of the car from the negative terminal of the battery and connect the multimeter as shown in the image below.
Once the contact is made, the car’s systems will wake up and so a jump in the multimeter reading will be observed. It will then come down to a more stable reading. If the ammeter is reading over 50 milliamps, something is using too much battery power and draining the battery. You can then remove fuses one by one in order of suspicion to find out which of them will result in a drop of the reading to acceptable level of below 30mA. The fuse(s) that are bad should be properly replaced as per vehicle procedure.


Easy right?
Better than taking your precious car to a trial and error auto electrician.
Knowledge makes a world of difference.

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