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If you have a .25 amp draw, it will drain the battery of 6 amps per day. If your battery was dead one day and just got a boost to get it started, it has to be recharged to be back to its 60-65 amp capacity, just driving it for a few kms will not recharge it and it will be recharged only to 10-15-20 amps capacity , the 6 amp draw per day will be enough to bring it back at a too low state of charge to start the car. dont forget that a lead acid battery looses about 50% of its power at 0 degrees.
You need a miliamp meter to check the drain, you have to open the hood,lock the car , wait a few minutes and then plug in the miliamp test meter in series with the neg battery post without loosing the circuit. that means plugging one wire of the meter to the car negative cable and the other wire of the test meter to the battery post and removing the car cable from the battery post without breaking the circuit, you will get the reading of the power drain.
 

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Discussion Starter · #82 ·
If you have a .25 amp draw, it will drain the battery of 6 amps per day. If your battery was dead one day and just got a boost to get it started, it has to be recharged to be back to its 60-65 amp capacity, just driving it for a few kms will not recharge it and it will be recharged only to 10-15-20 amps capacity , the 6 amp draw per day will be enough to bring it back at a too low state of charge to start the car. dont forget that a lead acid battery looses about 50% of its power at 0 degrees.
You need a miliamp meter to check the drain, you have to open the hood,lock the car , wait a few minutes and then plug in the miliamp test meter in series with the neg battery post without loosing the circuit. that means plugging one wire of the meter to the car negative cable and the other wire of the test meter to the battery post and removing the car cable from the battery post without breaking the circuit, you will get the reading of the power drain.
Agree, when the battery was mysteriously discharged overnight it was at 6.4 volts in the morning and so would not start the RAV4 P. The battery was removed, connected to a charger, charged to 13 plus volts and then load tested - so battery failure was not the cause of the overnight discharge.
Thanks for the caution on maintaining the circuit when measuring parasitic draw. I discount parasitic load a a cause of the over night discharge because, when the vehicle was idle and not plugged in for 4 days, the observed voltage drop was about 0.2 volts but this could have been be caused by temperature change of the battery or taking the initial reading too soon after the battery came off charge. Cheers
 

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Thanks for the advice. How can we check that the RAV4 P is in sleep mode ? The drivers display appears to be "off". The battery maintainer is connected after the power is switched off.
Incidentaly, I was informed by a Toyota technician that the vehicle likely has a residual load of 150 to 200 milleamps which would completly discharge a 100 amp-hr battery in 100/0,2 = 500 hours = 20 days.
Sounds about right if the 12v Aux battery was always fully charged, but if the 12v is only at 12.2v that is only 50% charged, so... only about 10 days. Les than that if OBD scanners, Dash Cams, or media players remain plugged in.

dp
 

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Could I use a multimeter attached to the positive connector inside the Jump Starting Terminal Cover under the hood, and a ground of course, to check the 12V battery voltage? Instead of going directly on the battery.

This looks like it could be used for hooking up charger.

Tom
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Could I use a multimeter attached to the positive connector inside the Jump Starting Terminal Cover under the hood, and a ground of course, to check the 12V battery voltage? Instead of going directly on the battery.

This looks like it could be used for hooking up charger.

Tom
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I don't see why not. In theory it should be the same voltage but with some minor losses. It may be worth comparing if there's a measurable difference between the reading at the battery terminals and the reading at the jump terminals.
 

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I don't see why not. In theory it should be the same voltage but with some minor losses. It may be worth comparing if there's a measurable difference between the reading at the battery terminals and the reading at the jump terminals.
Can I just connect the multimeter to the cigarette lighter w/ an appropriate adapter? I would like to test the rate of discharge after the car has just finished charging but with the charger still connected.
 

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Can I just connect the multimeter to the cigarette lighter w/ an appropriate adapter? I would like to test the rate of discharge after the car has just finished charging but with the charger still connected.
You can check voltage anywhere. The only way you can check amps draw on the battery is at the battery with the meter connected in series.
 

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Could I use a multimeter attached to the positive connector inside the Jump Starting Terminal Cover under the hood, and a ground of course, to check the 12V battery voltage? Instead of going directly on the battery.

This looks like it could be used for hooking up charger.

Tom
Yes, you can check using those points. They are direct/unswitched contact to the 12v Aux battery. That is also where I connect a smart charger to top off the 12v overnight once in a while.

dp
 

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Can I just connect the multimeter to the cigarette lighter w/ an appropriate adapter? I would like to test the rate of discharge after the car has just finished charging but with the charger still connected.
I did not check the cigarette lighter locations , but I assume they are switched, so no voltage reading unless the Prime is in Ready or ACC mode.

If they are unswitched, then yes.
dp
 

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Can I just connect the multimeter to the cigarette lighter w/ an appropriate adapter? I would like to test the rate of discharge after the car has just finished charging but with the charger still connected.
I would like to add: checking the rate of discharge right after a full charge will yield a false result, because there would be a steady discharge even if there was no load at all. The actual voltage should be stable after 24h. But unless you disconnect the 12v battery, this is not really doable.

dp
 

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I would like to add: checking the rate of discharge right after a full charge will yield a false result, because there would be a steady discharge even if there was no load at all. The actual voltage should be stable after 24h. But unless you disconnect the 12v battery, this is not really doable.

dp
I'd like to measure battery voltage immediately upon charge completion, then retest perhaps every few hours or so while leaving the charging cable connected the whole time. What is the source of the steady discharge you refer to, when does it commence, that you're suggesting slows down or stabilizes after 24h? Is the battery the easiest/quickest unswitched place to connect to 12v?
 

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MILLAMP test will give you an immediate result as if there is a drain or not, if yes, you can start pulling fuses one by one to see if you can find what circuit is the culprit. you cannot do this with a voltage test.
 

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Thanks for the advice. How can we check that the RAV4 P is in sleep mode ? The drivers display appears to be "off". The battery maintainer is connected after the power is switched off.
Incidentaly, I was informed by a Toyota technician that the vehicle likely has a residual load of 150 to 200 milleamps which would completly discharge a 100 amp-hr battery in 100/0,2 = 500 hours = 20 days.
Are you parking in a garage and not locking the vehicle?
Some newer cars (and I believe the Prius Prime and possibly R4P) drain the battery more if it is not locked - it keeps the vehicle in a closer to ready state. Locking it puts it "more to sleep". I haven't checked the R4P manual, but am pretty sure it was in our Prius' (if not it was a previous VW, that I'm remembering).
 

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Hey Folks, best/easiest spot to connect a multimeter to test 12v charge status with the car off? Would the + jumper cable connector in the fuse box be good?
 

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Well...interesting findings that I don't know what to make of! Here's what I did:

The car was at zero Soc for the TB when I did this short experiment, ambient temp 37F, doors locked, key fob NOT disabled. Car was built June 2021.

Prior to connecting the OEM 120v EVSE the 12v battery voltage was 12.43v
Immediately after connecting to charge: 12.63v
1h after charge complete but w/ EVSE connected: 12.39v
3h after charge completed w/ EVSE connected: 12.55v
6h after charge completed w/ EVSE connected: 12.47v
NOTE: multimeter remains connected during this time, however turned OFF except when checking voltage.

I needed to use the car so stopped the test earlier than planned. Took a short trip, returned then reconnected the EVSE to top off the charge which only took an hour or so.

Now here's where it gets weird! After re-charging to complete, I disconnected the EVSE. I reconnected the multimeter and again kept if OFF except when checking voltage.

12v battery now: 12.29v. Hmm, okay whatever! Ambient now around the same, 37F.
1h later: 12.17v
4h later my wife hears a funning hum coming from the car when she went out into the garage for something. I went out, retested voltages, now 12.09v. I disconnected the multimeter and the hum stops. Apparently it did not like keeping the MM connected even though it's absolutely turned off--at least the switch is off and display is blank.
This morning I just checked: 12.07v. I hope the car starts :oops:

Apparently keeping the MM connected is not a good thing even though it is turned off. Hard to draw too many conclusions here but it certainly seems like keeping the EVSE connected after charging completes demonstrated at some level 12v battery voltage actually went up, though dropped down slightly at the 6h post charge complete check. If the car starts I will try the test leg where we disconnect the EVSE and check 12v battery after charging complete, except will disconnect the MM as well except when testing.

Cheers
 

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Discussion Starter · #98 ·
Well...interesting findings that I don't know what to make of! Here's what I did:

The car was at zero Soc for the TB when I did this short experiment, ambient temp 37F, doors locked, key fob NOT disabled. Car was built June 2021.

Prior to connecting the OEM 120v EVSE the 12v battery voltage was 12.43v
Immediately after connecting to charge: 12.63v
1h after charge complete but w/ EVSE connected: 12.39v
3h after charge completed w/ EVSE connected: 12.55v
6h after charge completed w/ EVSE connected: 12.47v
NOTE: multimeter remains connected during this time, however turned OFF except when checking voltage.

I needed to use the car so stopped the test earlier than planned. Took a short trip, returned then reconnected the EVSE to top off the charge which only took an hour or so.

Now here's where it gets weird! After re-charging to complete, I disconnected the EVSE. I reconnected the multimeter and again kept if OFF except when checking voltage.

12v battery now: 12.29v. Hmm, okay whatever! Ambient now around the same, 37F.
1h later: 12.17v
4h later my wife hears a funning hum coming from the car when she went out into the garage for something. I went out, retested voltages, now 12.09v. I disconnected the multimeter and the hum stops. Apparently it did not like keeping the MM connected even though it's absolutely turned off--at least the switch is off and display is blank.
This morning I just checked: 12.07v. I hope the car starts :oops:

Apparently keeping the MM connected is not a good thing even though it is turned off. Hard to draw too many conclusions here but it certainly seems like keeping the EVSE connected after charging completes demonstrated at some level 12v battery voltage actually went up, though dropped down slightly at the 6h post charge complete check. If the car starts I will try the test leg where we disconnect the EVSE and check 12v battery after charging complete, except will disconnect the MM as well except when testing.

Cheers
Thanks for the test and report.
What do you think was the source of the "funny hum",
 
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