2000 Toyota Camry battery drain

I have a HIGH amp battery drain.
Over 6 Amps anyway for sure. (Thats the limit of the Voltage and Current controlled power supply I use for charging dead batterys anyway).
Here’s the rub. After disconnecting the negative battery lead, and then charging the battery overnight, I looked at the Power Supply displays, and the battery read 14.2V…Whch is where I set it to lower the current, if the battery was able to charge to that voltage. I connected the negative lead back up. All looked well. Still 14.2 volts, almost zero current draw. Then suddenly, and with no accompanying lights or sound, the power supply started drawing the max of 6 amps, and the voltage dropped to about 13.8 volts. (battery is now connected in parallel with the Power Supply). This went on as I scratched my chin for a minute, then the P.S. went back to 14.2V, 0 amps, and continued to cycle on and off that way every 2 minutes!!! HUH?!
(No after-market anything added)
Ideas? Thoughts?

When you say “no aftermarket anything” it says that you have not completely disconnected the battery when charging. Do that. It eliminates some variables.

I was trying to keep from writing a book.
Yes, I did let the power supply alone run the car. Same deal, too heavy a load to not max out the power supply, 6.8V and 6A, then toggled from that to, 14.2V about 5 mA, about every 2 minutes.
But good point. It is a strong about 2 yr old Interstate Battery, clean contacts, and all cells in the normal zone, electrolyte-wise. This problem happened very suddenly. Something is drawing I’m guessing over 10A, when it happens, cycling 50/50 on-off time at about 2 minutes each state.

I am concerned about any of your tests with the power supply in the circuit. A good power supply should have overload protections that might kick in. It could also be interacting with the car’s protection systems.
I don’t think you have clearly told us the symptoms you had when the whole problem started. Charge the battery (when it is completely disconnected), tell us what voltage it has reached, and then tell us what happens when you connect it in the car…ignition off for a couple hours…and measure the voltage then. Then start the car and take measurements. Voltmeters and ammeters, not power supplies.

However, as I already mentioned, it is a both Voltage and Current controlled supply. It’s A Lab P.S.
It is a 4 output supply, 2 of which can be placed in serial mode to get to 60 volts @ 3 amps, or in parallel @ 30 Volts 6 Amps. This is done just by selecting it on the front of the unit. So you can short positive to negative in any mode. and it will limit itself to the output currents above.

However I am fully aware that their are others who have more experience working on this specific car, and may have seen this before. Also, just bouncing ideas back and forth is very conducive to getting ideas on what might be done next to narrow down the problem. I have been repairing cars since I owned my own beater at age 16. I have almost never brought any car to a shop, friends cars included,
I am very mechanically minded, & have done all my own repair and preventative maintenance work.


I don’t think you have clearly told us the symptoms you had when the whole problem started. Charge the battery (when it is completely disconnected)

My response was:

This means the car was running just fine, no symptoms until I went to go to the store one evening.
Then the battery was dead enough to not run even a dome light.

That info was there also:

I don’t need to let the car sit for a couple hours, the power toggling starts immediately again, with or without the power supply in parallel with the battery. With that high a current draw toggling on and off,
I am not going to let the car sit and kill the battery again, damaging it even further. Last night I just left the supply on the battery at 14.4 Volts, when I looked at it this morning, it was at it’s normal float voltage, 14.4V. You may have noticed I upped the charging voltage to the 14.4 Volt I usually use for lead acid battery’s. The current draw was about 250mA, no load.
When the supply is out of the system completely, and the battery is not connected to anything, it settles to 12.8 Volts. So the battery has not been killed yet, I caught the problem fast enough to keep it healthy.

Take an infrared thermo gun and point at the fuses as the current draw is occurring.

The fuse that reads hotter than the others is the circuit with the current draw.


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Now THERE is a good idea! With that kinda amp draw, something is going to warm up! Now I just need to procure one…
Until I do get one, still open to anyone who has had anything similar or other thoughts…
Thanks Tester!

Symptom: your first symptom was that battery was so dead that dome light wasn’t on. That sounds like something that occurred while the car was parked. I am still asking what the battery does when it sits now…have you measured parasitic drain at key off?
Your second symptom is “power toggling”. I am not quite sure what you mean by that. Is it a variable idle speed?
You and I agree that we learn a lot more by diagnosing these things ourselves. It totally helped me supervise the repairs of some million dollar hospital equipment. (No, I did not do them myself, so nobody got killed.)

You should be able to find the fuse circuit with the trouble by removing suspected fused circuits one fuse at a time to see if the problem goes away. Since the ignition is OFF when the trouble happens the trouble should be tied to the fuse panel under the hood. Start with the higher amperage fuses.

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Searching for a draw based on the charge rate of a battery charger is “tail chasing”.

The amperage draw must be measured in series with the circuit.

I am not trying to diagnose the problem by seeing what the Power Supply is reading.
But it DOES SHOW that the problem is happening when the battery
with the power supply across it initially reads 1/4 Amp, then goes to it’s 6Amp capacity. It simply shows me that the problem is happening, and has the added benefit of keeping the battery charged, especially when the problem is not there, and you can tell it is keeping the battery from draining/ getting damaged. I may be crazy, but I’m not stupid. ALL testing measured here has been with the car keys not even in the ignition.
FYI: I have put my DVM in series (In 10Amp current mode) with the battery, no charger involved, and it blew the 10Amp fuse in the meter. So after replacing that fuse, I keep the power supply across the battery as a crutch. At least I can see when the problem is occurring without hurting either the meter or supply.

You keep asking questions I have given answers to. And I’m sensing some snark. Give me a ham on rye, hold the snark. I am a Electrical Engineer, and can hold my own in troubleshooting. But often bouncing ideas off others is helpful, (sometimes not I guess) And many times you will find somebody who has had the same problem, and can save you much time. While I need this car fixed, I have another available, so it lessens the pressure/ urgency of completing the job.
The car has one symptom; 1) When the engine is off, I have a battery draining. Clearly the car is fine while running, or at least whatever the problem is, is getting masked by the additional amperage from the working alternator. All the measurements given here were with the keys out of the ignition. Letting the car sit for even a short period will just result in the battery getting further damaged. Unless of course I either A) keep the P.S. on it, or B) disconnect the battery as soon as I get out of the car.
I measured the battery once with the engine running, It was 13 point something volts, and rose when I manually increased the RPM under the hood. Since I know that the charging system is working, I will be doing all my trouble-shooting with the car off.
Tonight I will be borrowing a friends IR Thermometer, and see if I can do some narrowing down with that, first under the hood of the car. With luck that will get me to the Fuse Box inside the car.
(Thanks for that idea @Tester)

An “Electrical Engineer” should know the difference between a “Power Supply” that you are using and a “Battery Charger” that you should be using, are not interchangeable.

An “Electrical Engineer” should know that just because an alternator is putting out 13.6 volts, doesn’t mean it’s putting out any amps.


I imagine I will be getting to that method if once I get the IR Thermometer, and am still unable to find anything. My concern with the IR Thermometer, the focal point may be too large to be of much value in a crowded fuse box. What would be of real help would be a IR camera. As it is intermittently drawing (I’m guessing here), between 10 and 15 amps, I should be able to find some heat somewhere there shouldn’t be any! Thanks for the input.

Sir, let me state up front that I am not mechanically, electrically, or electronically knowledgeable. So please ignore me and accept my apology if my comments are irrelevant.

However…your mention of the power drain toggling on and off sounds remarkably like what killed the battery on my cell phone awhile back. It turned out that a glitch had the phone actively pinging for system and app updates every minute despite being set to check only once a week.

I have no idea what system or onboard computer in a car could possibly be trying to activate anything. And I realize the idea is almost certainly not relevant.

But it is that consistent, repetitive toggle on and off of a parasitic power draw (if I’ve correctly understood your problem) that sounds so familiar to what killed my cell phone battery.

No, your not wrong, the effects are similar, but your right again, in that there is no real relation with the problem my car has. Cell phones are often used as repeaters to extend signals from other’s phones to weaker signal areas.
That kind of thing will definitely shorten your battery’s charge time.

Well, it was a wild guess. I admit I didn’t see how it would apply to cars. But the symptom and drained battery result seemed familiar so I mentioned it just in crazy chance it had any relevance.

Good luck solving your problem. I am interested to learn what turns out to be the cause and resolution.

You would see a square wave riding on a lowering DC level, as the load was alternately draining at around 15Amps, then back to it’s float voltage, (Not draining) at a 50% duty cylce, 2 min draining, 2 min decreasing float voltage.
Just imagine there is a gremlin in the car putting a 1.2 Ohm resistor across the battery every 2 minutes, holding it there for 2 minutes, then releasing it, rinse and repeat.

Thanks, and once I’ve found the issue, you will find the answer here!

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If the draw is to high for your meter, use a 12 light bulb in series with the battery. The higher the draw, the brighter the light. Keep pulling fuses until the light dims considerably. At least then you will find which circuit is the problem. Then you can start narrowing it down.