Trying to pinpoint what is draining my battery

Hi there,

I recently posted a situation where my 2001 Neon wasn’t starting in the mornings as something was draining my battery out overnight. A red flag has been realized as of recent. The clock on my radio inside the car has intermittently been staying on when the car is completely turned off, or blinks off and on when the engine is off. The last few days it’s been warmer and dry outside and the clock has been doing what it should, turning off when the engines off. We now have wet rainy weather happening and the clock has started blinking again. My battery drain situation has to be tied to this component somehow. I went and took the fuse that is connected to the radio out this evening. Should that help until I can get the car back in to be looked at?? In other words, will taking this fuse out disable the radio component and stop it from draining my battery?



I can’t quite understand what you are saying about the clock. Do you mean the clock display is staying on when the car is off, whereas it normally turns of?

But something is draining your battery overnight? How low is it in the morning when you try to start the car? Completely dead, dash lights off? I assume you get the car jumped in the morning?

Whatever the original problem, there is a good chance your battery has been damaged by this time, so whatever the final fix is, you will need a new battery. Even if taking the fuse out would fix the problem, the battery may be so damaged that it won’t hold a charge anyway.

I doubt that your clock or even standard factory radio would drain your battery overnight. Keep in mind how long a transistor radio will run on one tiny 9V battery. If you have a big non-factory amp, that would be another matter. There may be something else on that same circuit that’s doing it too. You can try pulling that fuse to see if it still drains, but also look for lights that are staying on. The trunk and glove box are two that might do it.

it’s not the radio, but the display on the clock, which can use up a bit of current. Although not that much. To kill a good battery over night, you would need several to 10 amps of drain. But if the battery is damaged, a few amps could kill it.

Marian, I suggest you take the car somewhere and get the battery tested. If it’s OK, you might get a small battery charger, perhaps $25, to keep the battery alive at night while you troubleshoot this problem.

A clip on ammeter will tell you what the battery drain is when the key is off. This is called “key-off current”. It should be in the 50-100mA range. Wait till the car has been turned off for an hour before measuring, as some modules take time to power down. If the key-off current is excessive, then you can start pulling fuses to narrow down the problem area. Be aware that opening a door or pulling a fuse may reset the modules timers and cause a higher off current for a while.

A point that you may not be aware of: there are many electronic modules in a modern car that draw current when the power is off, including the radio, the computers, the security system. Typically they lower their current drain after the key has been off for an interval (interval varies with design).

Hi again Bill,

It’s the clock display on the radio in the car that has been acting funny. Wet, damp weather seems to be causing the clock to go haywire. My battery worked fine the last two days. The car has been running fine and the clock has been working well in the nice weather, up until today with the weather change. My battery seems to have survived being drained so far. With my clock starting to blink again today, it was my expectation that I would wake up to a car that would have trouble starting. You can read my previous posts under “electrical problems?” that will explain how my car has been acting recently.



Are you for hire??? ; )


no, but there are lots of competent mechanics out there… Check

you think the clock is the cause of the problem, and possibly it is.

However, could not the problem be a current drain somewhere else in your car, and when the battery gets low enough, it causes the clock to lose it’s memory and start flashing, just like when you pull the plug on a microwave and plug it back in?

It’s not likely at all that your radio or clock has anything to do with a battery drain.
The first thing to always check is to make sure the trunk light is not staying on.
After that, it requires a bit of electrical digging.

The battery negative cable should be disconnected and a VOM or test light connected between the battery terminal and the battery cable. Fuses should be pulled one at a time until the light goes out. This will narrow it down to a particular circuit. After that it gets stickier.

If the VOM shows a reading or the test light is still on with all of the fuses removed, then you have to start considering an alternator problem or something that is wired through a fusible link.

Testing for a parasitic draw from the battery is a little more complicated on todays vehicles. That’s because there are many electronic modules that stay awake after the ignition is turned off. If you just remove the negative cable and connect either a meter or test light the modules can reawake. This of course is going to show a current draw from the battery.

Some of these modules can stay awake for as long as forty minutes. So if you do this, wait at least an hour before you test for a parasitic current draw. Or if you don’t want to wait, connect the meter or light in this manner. Poke the meter/light probe into the negative battery post and connect the other lead to a ground. This creates a secondary negative connection for the battery. Remove the negative battery terminal. Place the terminal on top of the battery post. Slide the terminal across the top of the post until you reach the meter/light probe. While holding the terminal down on top of the post, remove the meter/light probe from the post. Slide the terminal the rest of the way across the top of the post, and reinsert the meter/light probe. Now the battery terminal can be removed and you can immediately check for a parasitic current draw from the battery.


Much easier to use a clip on ammeter. Also, if you use your technique, with a heavy drain, most of the battery voltage will appear across the trouble light, leaving only part of the 12 volts across the load. This interrupts the circuit and resets everything.

Not sure that is clear. When you connect the trouble light in series with the battery, the 12 volts from the battery is split, some of it across the trouble light, the rest across the load (the auto’s electronics). What the split is depends upon the loads. If most of the voltage is across the trouble light, ie, it lights, then there is little voltage across the load, ie, the auto, and everything resets.

The best way to test for a draw is to install a switch between the battery cable and the terminal. Install a ammeter in parallel across the switch. The vehicle manufacturer now has specs for how long to wait for the modules to power up, most specs I’ve seen take are from 15 to 30 minutes.

After the modules power up you open the switch and let the system operate thru the ammeter. The most common spec for a amp draw is 050 milliamps.

The most common misconception is that you can use a test light to check for a draw. That is wrong. You have no idea how many amps are needed to light the test light. You have to see how many amps are being drawn to know for sure. If you look up the service procedure for amp draw testing a test light is not used or even mentioned, it’s always a ammeter.

I normally use a test light and don’t have a problem with this method at all. It’s never failed me yet and is simply a matter of noting how brightly the test light filament is glowing. If there’s a draw worth worrying about the lamp will be moderately bright at a minimum.

At times I’ve even used an old Chevy door chime. A weak draw will not trigger the chime but a problematic draw will set the ding-donger off. Kind of helps if you’re under the dash and can’t watch a VOM or test light.
The irritating ding-dong also provides incentive to work faster. :slight_smile:

I agree, it can work but if someone with little or no experience uses a test light they might not be able to interpret the the results as you or I might. Plus I think both of us can agree that a test light could work on older cars with less electronics. Todays car with all of the electronics and modules need a more specific method of testing, that’s why I would follow whatever the car maker says to do.