How Do You Diagnose a Car Battery Drain?

How do you diagnose a car battery drain? Welcome to the Mercie J, where compassion and craftsmanship come together. I'm Rick Smith.

So when you talk about a battery drain we mean that when you have the car sit overnight or perhaps for a couple of days the battery’s dead.

So first of all, we need to make sure that our battery is healthy and that the alternators are working and the rest of the car is fine. But if the battery is going dead overnight or after it sits for a couple of days, then something is on all the time even when the car's off.

So if we have the battery drain overnight, typically that's something fairly big so we want to maybe look for one of the visor vanity lights or a light on in the trunk or something left on.

If the battery takes 2 or 3 days sitting to go bad, then that's gonna be a little tougher. So what we do in the shop is we use an ammeter. And so this is an ammeter that clamps around a wire.

This was a digital multimeter that works in series. But regardless what we do as we check to see how many amps are pulling on the car when it is turned off. And it needs to be at rest for 20 to 30 minutes typically, because all of the computers need to go to sleep or shut down and then we can see.

Typically the maximum amount allowed is 50 milliamps on the average car. If we have say a 100 milliamp draw that's pretty small, that’s gonna take a few days, and will most likely maybe be a module not going to sleep or something like that.

But if it goes dead overnight, that's gonna probably be closer to a couple 100 milliamps, and that will sometimes be a light bulb or something that's left on. And then after we see that we have too much draw, now we have to find that and so we need wiring diagrams and we can do voltage drop test and there's a number of ways for us to try to get down the road to find it.

So I hope this has been informational to you till next time, safe travels and blessings to you.

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