Modern cars with lots of electronics always have battery drainage even the engine is off. Electronics will go to sleep mode, but it will still consume a little. I have designed many electronic accessories and decided to check if there is any effect on battery life. My test car is the 2017 Mazda MX-5 RF Launch Edition. It has a SmartTOP module installed as well as my front camera kit, ACC controller, and automatic footwell light.
Measuring current accurately is a little tricky because any circuit interruption will wake up all electronics again. Also range from 10A to milliamps. To avoid these issues, a circuit switch is really handy. I found a good option on Amazon. Because I’m often testing new electronics, I found that having this device installed is time-saving.
Now, when the switch is in position “Power on” I can safely attach the multimeter and after 2 minutes switch can be disconnected and a small current will go through the tester.
The proximity of Key Fob seems to have no effect on this test, however when the car was locked, this current drop to about 15mA, which is a very little drain.
This means if the car is unlocked for a long time, it will drain the battery faster.