Unsolved Battery Drain (with detailed troubleshooting)

lock yourselfs inside the car then lock and than check amps

 

1. Put a charger on the 12V battery for at least an overnight period, so that it doesn't deteriorate further.

2. Reinstall all parts that you had previously pulled for testing.

3. After the battery has been charged, reconnect it to the car.

4. Open the driver's window so you can easily enter the car if you have a problem with the door locks.

5. Open the hood. Remove the cover over the main relay/fuse box near the inverter. To do this, push hard on the latch at the front of the cover, then pivot the cover up and remove it.

6. Open the red cover over the dedicated positive jumpstart terminal. Find the 10 mm nut that secures the positive battery cable to the stud and remove it. Use long nose pliers to pull the cable up from the stud.

7. Turn off the two cabin overhead lights and the hatch light, using the switches. (The reason for doing that is to avoid further current draw when you open a door or hatch - since your ammeter typically is protected by a 10A fuse.)

8. Close the hatch and all doors and lock the car.

9. Put the current meter in series between the stud and the cable. (I assume you do not have an aftermarket alarm which monitors whether the hood is open or not.)

10. Observe the current flow, wait a minute or so. If the quiescent current draw is over ~20 mA, you have a problem.

11. Start pulling relays in the main relay/fuse box, one at a time, to see whether that has any impact on the current flow. If you find a relay that impacts the current flow, test it with a 12V source and your ohmmeter to see if it is stuck in the closed position. If so, replace it.

12. Note that you can find relays in the main relay'fuse box, in the relay box over the engine, and under the instrument panel on the driver's side. Try to keep the doors closed when you are doing the testing. An open door will cause the body ECU to activate and wake up other ECUs, potentially also powering up the brake actuator motor. Obviously all of that will impact the current draw.

 

The reason for the gradual fall in current drain from 1.5 amps to 1 amp is because the current drawn through a given load is a function of the voltage applied. Basic Ohms law. Current flow in amps (A) equals the voltage (V) divided by the load resistance in ohms (R).

So A=V/R
Using your figures beginning at a load of 1.5 A = 12 V/8 ohms
when battery voltage falls after discharge 1 A = 8 V/8 ohms
As the voltage falls so will the amps.

The load resistance will alter with temperature difference especially if it is a light bulb as the resistance of most metals goes up as the temperature goes up so a hot filament bulb (giving out light) will have a higher resistance than when it cooler (running on a voltage much lower than it's design voltage) but this is ignored in the formula for clarity.

John (Britprius)

 

WOW! Some really fun stuff here First off, you can't break the circuit between the battery connections and get
a proper amperage reading. The ECM and other control modules will power up every time you reconnect it with the meter. You're gonna need a switch between the negative post and the cable to do a proper parasitic load test.

You need to install the switch and close it. Start the car can allow it to run for a minute. Shut it off and hook the meter across the switch like my drawing shows. Turn the meter on, close all the doors and reach in through a window and open the switch. Check the amperage draw and wait for it to drop. It drops as the computer control modules go to sleep.
Some take up to 20 plus minutes to shut down. Your amperage draw should drop to anywhere from 20 m/a to 50 m/a.
Anything over 50 m/a should be considered an excessive draw. In a perfect world a 35 m/a reading is ideal.
You can also trip the latch on the door/hatch and leave it open to gain access to the battery. As long as it turns off dome lamps, it's okay. You can't disturb the system while the switch is open or it could blow the meter fuse. It will also power up the modules. Make sure and remove the key from the car and place it far enough away that it can't detect it, or it will keep the system active. I suggest you get your good meter working for this job.

 

Yes, if you can devise a way to keep the driver's door switch in the "closed" position that would be fine.

The Smart fob needs to be at least 15 feet away from the car when you are ready to measure quiescent current draw. If it is closer, it will start to communicate with the car which will increase battery current draw as the Smart ECU, body ECU and immobilizer ECU power up. I believe you will find that the quiescent current draw will be reached after just a few minutes.

I have had to replace the LCD display on my Fluke 87 once so far. A few of the elements are starting to not be as dark as they should be, so I may need to order another from Fluke soon.

Until you obtain a new display for your Fluke, you might try cleaning the display border with isopropyl alcohol to see if that helps improve the conductivity between the display and the DMM display circuitry.

 

Auto engineer I have the same opinion as you with the Exide battery. Even more so in the UK where the Optima is more than double the price of the Exide. I do not however use either battery opting instead to use a AGM mobility battery of the same size but rated at 62 AH capacity.

John (Britprius)

 

I take it that you have not tried to measure quiescent current draw yet?

 

If the battery has a shorted cell, then 12.5V would be about as high as it is going to go. I would expect that the battery would tend to feel a bit warm afterwards, as most of the charge is dissipated in the electrolyte.

There have been reports of premature 12V battery failure here, so it does happen.

 

Any further updates on the Exide? I suspect mine (still the original) might need replacing in the next few months and so I am curious. TIA.

 

"Resting voltage is over 12V after an overnight sit."
Well, how much over 12V? If 12.1V, this is pretty bad. If 12.9V, then your battery is great. I suggest that the battery should be fully-charged, then see what happens after it rests overnight.

 

12.5V is not very reassuring. My 4.5 year old OEM Yuasa reads not drastically lower (~12.2 this morning). This is right after I get into the car which means the brake actuator had just run to completion before I checked my ScanGauge II. Per others' instructions here, whenever I get a replacement, I intend to:

1. Make sure it's at least 12.9 V to begin with.
2. Put my CTEK MUS 4.3 on it overnight.
3. Make sure the resting voltage after a day after disconnecting the charger is in the 13.1 to 13.2V range.
4. Install the battery.

Perhaps, you can run thru the above over a weekend and see if you end up with a over 13V resting voltage? If you do see 13V but then see 12.5V after a few days of using it in the car, perhaps there's some unusual draw in your car or your inverter/charger has an issue?

 

Also, you might compare yours to the below where 12.5V is reported while in Accessory mode:

12 volt battery for 2009 Toyota Prius | PriusChat

There seems to be at least a 0.2V difference between yours and paphylliman's and that too considering he is in Philly and you are in the much milder SF Bay area.

 

Also, how long are your trips? If they are very short, that might explain the lower battery voltage.

 

Highly likely that neither of those things will be possible.

The "nominal" voltage of a wet cell battery is 12.6.
Recent formulations seem to have raised some to 12.8.

You will never see above 13 except immediately after a charge......or in the car with it running.