# Parasitic Drain on 12V Battery for Plug-In Hybrid not making any sense



## de-nagorg (Feb 23, 2014)

richapple said:


> My method of testing the battery draw is to have the 12V starter battery (on a plug-in hybrid) completely charged, and to remove the 12V battery ground cable and have the multimeter set to the 10 Amp position and the red lead connected to the 10A jack. The ground cable is then a few inches from the ground post on the battery and I touch the red lead to the ground cable metal and the black lead to the battery’s ground post.
> 
> I’ve done this many many ways (car locked and the engine hood tricked via tripping the hood latch so it can be open and have the car think it’s closed, car unlocked, car fob far far away, car simply off but surely active in some ways, hours given before testing so the car has thoroughly gone to sleep…) and generally the measured draw is over 2 amps every time. About 2.15 Amps locked, 2.3 Amps when unlocked (and always there’s a bit of jumping around for those numbers on the digital readout).
> 
> ...



The drain is one of the electronic gizmos on the vehicle.

Digital clock used to be a major draw, in the 80's, there are many other additions on modern vehicles, alarm, the mileage calculator, the compass, temp gauge, all the little nags that annoy us.

Could be any or all of them.

Isolating one at a time is the only way to solve the puzzle.


ED


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## GrayHair (Apr 9, 2015)

Do you know what devices other than the starter are connected to the starter battery?

I prefer to troubleshoot in halves; divide the "circuit" into 2 approximately equal halves, disconnect one half (pull fuses) and see if the problem still exists. Repeat halving in the part of the circuit with the problem.

I found that on gas burners, pulling the fuse on some items increased the current draw.


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## ukrkoz (Dec 31, 2010)

Question is pointless without knowing, which hybrid it is.
12V IS NOT STARTING THE ICE. OR CAR. On hybrids, 12 V is backup power storage for electronics and SHOULD have continuous power supply to them. 12V is charged by traction/hybrid battery. By removing and reconnecting 12V battery, you are asking for helluva trouble eventually, as hybrids do not like that. 
For Toyota hybrids, if your 12V is below 11.7V, it needs to be recharged or, better off, replaced.
Stop messing with battery cables. Please. It ain't g'ol 1967 Chevy pickup.


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## Brainbucket (Mar 30, 2015)

I use a 12v test light to diagnose draws. Put it between the negative post and the disconnected negative terminal end. If it lights up, you have a draw. If it flashes, you have a module that's still awake and not going to sleep. They all should go to sleep in around 5-10 minutes. But the 12v battery is not the starting battery.


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## gthomas785 (Mar 22, 2021)

I'll just pop in to mention that battery voltage is not linear with charge - fully charged is around 13.6V  _Edit - typo - I meant 12.6V_ and fully dead is around 11.7V.
Measuring "12 volts" does not mean your battery is charged.
Have a nice day


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## richapple (Nov 25, 2012)

I should usually lead a post/question with the clarification that I’m no expert or even that knowledgeable. Just trying to do it myself. But to add some info and maybe question a reply or two:

de-nagorg and GrayHair are right about how to solve the puzzle. And though I did some fuse pulling for likely culprits (and in old day computer programming the GrayHair “divide by half and look” and then isolate by zero’ing in by “rehalving” each result was also a way to search through values read by the program), finding the source of the parasitic drain isn’t really what I was asking. I’m trying to figure out if my Amp Draw measurement is flawed because at 2+ Amps, that battery should be drained down way too low to start the car just overnight (assuming it’s a 48 Amp Hour battery - fairly standard I read).

And again, what I just wrote about a 48 Amp Hour battery and what I think that means is very possibly way off the mark.

But ukrkoz saying the 12V on a hybrid is not a starter battery is confusing since “starter battery” is what oodles of hybrid explanations and forum comments seem to call it. I know when it’s dead the car is not going to start. And yes for sure that battery is giving continuous power to all the electronics that need power when the car isn’t running, But… This hybrid is a Subaru 2019 Crosstrek Plug-in Hybrid, and I do wonder now about the warning to not be removing and reattaching the ground cable on the 12V battery. I know lots of recharging by an external battery charger is not good for a battery, but disconnecting can be bad for the hybrid lithium battery? So "please" don't? Maybe I just won't anymore, and thanks for the "please." On my 2006 Prius I know replacing the weak 12V battery caused problems and I’d wished I’d used another battery or something to keep supplying charge for the "devices," but the only ill-effect seemed to be everything that I’d set that had to be remembered was no longer “remembered.” (’62 VW bug was like a 1967 Chevy Pickup in that it was pretty easy to understand…)

Brainbucket seems to agree that the 12V is not the “starting battery,” but Google does say this about Hybrid vehicles and their batteries: _…and a smaller 12-volt battery tasked primarily with starting the vehicle…_ So yeah, I’m a bit baffled by this.

gthomas785 shares good info, and the Panasonic 12V Subaru uses is reputed to not be a great battery to begin with. Fully charged via a battery charger I get 13.4 or so, but as I understand it “surface charge” means that’s not an entirely accurate read. Letting it sit after the charge for a few hours always then has it reading at 12.45ish Volts. And with how I’ve been torturing the battery, I do totally plan on getting a new, different battery once the drainage problem is figured out. But my original puzzlement was how an apparent (and must be wrongly measured by me) 2.3ish Amp draw isn’t sending that battery down to 11.7 or whatever where it will not start the car.

Thanks any and all!


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## Brainbucket (Mar 30, 2015)

I stand corrected.


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## User02 (Sep 17, 2015)

2.3 amps at 12.5 volts is 28.75 watts of energy being dissipated by some leaking component in your vehicle, that's like a 25 watt light bulb, and its going to warm something up significantly.. At that rate, a thermal imaging device could probably be used to see which component is a few degrees warmer than everything else. 

The only way this wouldn't work is if that 28 watts of energy was being distributed to a bunch of smaller items, which would indicate an accessory relay that powers that stuff has a pair of welded contacts.


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## LawrenceS (Oct 21, 2020)

2019 Crosstrek plug in hybrid, shouldn't it still be under factory warranty, unless you've put some serious miles on it. Take it to the dealer and let them deal with it if you've had starting issues after sitting for less then a week.

First to clear up some misinformation here.

Multimeter draw check is fine and you are doing it right. 

2.15a does sound high.

I highly doubt you will cause any issue by removing and ground cable multiple times.

Fully charged batteries are 12.6v not 13.6v. Yes when you get into the 11-10v range is when they act up but voltage isn't the best indicator of the health of a battery. Sometimes they will hold a slightly higher charge right after charging but that's just surface charge as you said. Unless there is internal battery failure, look up battery acid stratification if you want more info on that.

It's called the starting battery because it powers the 12v computer that controls the big battery/electric motor that is probably used to start the engine.

How long are you leaving the multimeter on the battery? I'd give it at least 10 minutes up to 1/2 hour for everything to power down. Also I'm assuming you don't have the plug-in charger connected which would probably keep a couple things awake to regulate charging of the big battery.


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## richapple (Nov 25, 2012)

LawrenceS said:


> 2019 Crosstrek plug in hybrid, shouldn't it still be under factory warranty, unless you've put some serious miles on it. Take it to the dealer and let them deal with it if you've had starting issues after sitting for less then a week.
> 
> First to clear up some misinformation here.
> 
> ...


Thank you, LawrenceS. Very clear, well stated information. The multimeter I have is "fused" for both positive connection jacks, and the 10A one says 10 seconds max for when using that jack and even that only do once every 15 minutes. It is an inexpensive multimeter and perhaps good ones can just remain connected for a half hour? I have left all doors locked and the fob key very far away and have given the car a couple hours for all to power down, and still the 2+ amps measurement. (fob key actually has a feature to hold one button and push another twice so it shuts down to save its battery - so that in addition to having the fob key nowhere near the car)

I've done the above both with the ground cable disconnected from the battery for the couple of hours, and also with the cable connected thinking perhaps it needs the 12V to figure out it's time to go to sleep. For the draw test in the second case, of course I had to disconnect it, but there is no evidence that is waking anything up.

And true, the plug-in charger isn't in play at all... Uh, either the external battery charger or the car's plug-in charging port...

As for the dealer, after the car wouldn't start without first charging the 12V - and that was just after a few days - we did take it in under warranty and their test reported a "draw" of just 35 milliamps. Within spec, as they say. My multimeter was up at a cabin, and due to fire danger we did get up there accompanied with the plug-in charger and even one of those battery-charged "jump starters" so we wouldn't get stranded.

In town now we'd take it to the dealer again, but I'm figuring I'd just be wasting there time, and while the one time the 12V was too low after a few days to start the car did happen, perhaps that was a fluke. If the battery charge would plummet down after a few days sitting, we'd take it in pronto. But it must be that yes the 2+ amps draw is dropping as stuff powers down, and none of my attempts to measure the draw without having the amp-hogs wake up and kick in again has actually achieved that.

Thanks!


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## User02 (Sep 17, 2015)

richapple said:


> Thank you, LawrenceS. Very clear, well stated information. The multimeter I have is "fused" for both positive connection jacks, and the 10A one says 10 seconds max for when using that jack and even that only do once every 15 minutes. It is an inexpensive multimeter and perhaps good ones can just remain connected for a half hour? I have left all doors locked and the fob key very far away and have given the car a couple hours for all to power down, and still the 2+ amps measurement. (fob key actually has a feature to hold one button and push another twice so it shuts down to save its battery - so that in addition to having the fob key nowhere near the car)
> 
> I've done the above both with the ground cable disconnected from the battery for the couple of hours, and also with the cable connected thinking perhaps it needs the 12V to figure out it's time to go to sleep. For the draw test in the second case, of course I had to disconnect it, but there is no evidence that is waking anything up.
> 
> ...


To disconnect the battery and reconnect through the meter without actually disconnecting the battery from the system, use a jumper wire as a switch. Jumper the bat terminal to the main cable, disconnect the main cable from the battery lug while leaving the jumper wire connected between them.. This way, whatever is seeing that 12 volt current won't be interrupted even though you removed the main battery cable. Now put your meter between battery and cable and disconnect jumper wire so all juice goes through the meter.


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## richapple (Nov 25, 2012)

Shopguy said:


> To disconnect the battery and reconnect through the meter without actually disconnecting the battery from the system, use a jumper wire as a switch. Jumper the bat terminal to the main cable, disconnect the main cable from the battery lug while leaving the jumper wire connected between them.. This way, whatever is seeing that 12 volt current won't be interrupted even though you removed the main battery cable. Now put your meter between battery and cable and disconnect jumper wire so all juice goes through the meter.


I did see somewhere in other related questions/answers on these DIY pages a Honda tech saying something similar. His method was to loosen the ground cable but have it connected still, came back and have the multimeter already connected while simultaneously lifting the ground from the terminal. Seems that would accomplish the same, but your method looks more solid. thanks


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## LawrenceS (Oct 21, 2020)

richapple said:


> I did see somewhere in other related questions/answers on these DIY pages a Honda tech saying something similar. His method was to loosen the ground cable but have it connected still, came back and have the multimeter already connected while simultaneously lifting the ground from the terminal. Seems that would accomplish the same, but your method looks more solid. thanks


Ah you found that reply I made 6 months ago to the sc430 thread.

The ground cable method is fairly easy, but it is dependent on the battery location/design. Some of the newer vehicles I work on the batteries are in trickier locations or the terminals sit in cutouts and there is minimal slack in the negative cable which would complicate it. But yes if you completely remove 12v power from a vehicle when it gets power back from hooking up a meter it is going to wake everything up, so to put the vehicle to sleep it cannot lose power.

Pretty sure the 10sec max 15 minute thing on your meter is if you are measuring amps close to the fuse rating as it could pop the fuse but at 1/5 of the fuse rating it should not cause an issue for hooking it up for an extended duration, but if you don't want to risk popping the fuse using a jumper between the cable and post while powering it down then hooking up the meter in parallel and removing the jumper after 10-15 minutes would also work.

Unfortunately at dealers we are paid by the repairs we make so if a problem cannot be easily duplicated or verified we have no incentive to spend an excess amount of time trying to duplicate it as we are not being paid to. The best advice I can offer would be taking photo's or video's of the draw showing on your multimeter to prove it is happening. Also if you can find any specific sequence of events that you do that might lead to it triggering the draw that would help the tech in duplicating it.


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## ukrkoz (Dec 31, 2010)

So you have inline "Toyota derived" plug in hybrid system. With plug in part simply being external hybrid battery charging while parked and with ICE off. As it is Toyota derived, system is pretty much same - moving wheels charge traction battery during deceleration, there is no starter, as motor generator starts ICE when needed, MG is fed by traction battery and 12V is charged by traction, aka hybrid battery. Far I know, Toyota designed them so that 12V is not charged, when traction battery is being charged or, when traction battery runs low on charge. Traction battery is most safe guarded. 
Just keep all that in mind, when approach your tests with "this is how we do it on conventional cars" methods, regardless, of which tech said what. 
If your 12V runs low - and I am aware of at least one Avalon hybrid that set unattended for almost 2 years yet, started fine after some hesitation - you either have parasitic drain exceeding electronics backup demand or, issue with 12V converter and charging system. You need a HYBRID mechanic to look at it. Not a "Honda tech". Any "tech" that advises you on anything must answer simple question - are you a hybrid technician or conventional vehicle one? 
I'd put a trickle charger onto that 12V and do load test on it, keeping in mind, it's a deep cycle battery and they are tested according to a special protocol. AGM deep cycle.


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## LawrenceS (Oct 21, 2020)

ukrkoz said:


> So you have inline "Toyota derived" plug in hybrid system. With plug in part simply being external hybrid battery charging while parked and with ICE off. As it is Toyota derived, system is pretty much same - moving wheels charge traction battery during deceleration, there is no starter, as motor generator starts ICE when needed, MG is fed by traction battery and 12V is charged by traction, aka hybrid battery. Far I know, Toyota designed them so that 12V is not charged, when traction battery is being charged or, when traction battery runs low on charge. Traction battery is most safe guarded.
> Just keep all that in mind, when approach your tests with "this is how we do it on conventional cars" methods, regardless, of which tech said what.
> If your 12V runs low - and I am aware of at least one Avalon hybrid that set unattended for almost 2 years yet, started fine after some hesitation - you either have parasitic drain exceeding electronics backup demand or, issue with 12V converter and charging system. You need a HYBRID mechanic to look at it. Not a "Honda tech". Any "tech" that advises you on anything must answer simple question - are you a hybrid technician or conventional vehicle one?
> I'd put a trickle charger onto that 12V and do load test on it, keeping in mind, it's a deep cycle battery and they are tested according to a special protocol. AGM deep cycle.


Honda Master tech, which includes Honda Hybrid training. Pretty sure it's not that much different then Toyota Hybrids.


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## richapple (Nov 25, 2012)

LawrenceS said:


> Ah you found that reply I made 6 months ago to the sc430 thread.
> 
> The ground cable method is fairly easy, but it is dependent on the battery location/design. Some of the newer vehicles I work on the batteries are in trickier locations or the terminals sit in cutouts and there is minimal slack in the negative cable which would complicate it. But yes if you completely remove 12v power from a vehicle when it gets power back from hooking up a meter it is going to wake everything up, so to put the vehicle to sleep it cannot lose power.
> 
> ...


Holy cow, the bright light popped on above my head (did anyone’s screen brighten upon seeing this comment?) and not only do I finally “get it” now (thanks LawrenceS The Certified Honda and Hybrid Tech Guy), but now all is successfully resolved.

The 2019 Subaru Crosstrek Hybrid does have its 12V right up under the hood, entirely accessible, so yes, the loosened ground cable still making contact and allowing time to let the car lullaby itself to sleep did come in at… just the .03 Amps draw, bouncing to .04 a bit. 30 to 40 Milliamps, which explains the battery never really suffering. (Well, suffering a bit because I disconnected and charged way too often, and I’m sure that’s not good for a battery.)

Unexplained is what the heck made the battery swing so low for our sweet chariot to not be able to start just sitting those few days right after a new DCM got swapped in by the dealer. My obsessing just ‘cuz of that one incident is kind of explained by our going up to the cabin in Wawona where you never know when the alert will come in to grab your things and high tail it from a fire.

As for Hondas, Toyotas, etc. - I thought my 1990 Honda Civic Hatchback was a great car, but when I wanted to get a hybrid of some kind in 2006, the Prius won out because its hatchback opens to a simple flat surface one can sit on to put on and take off a wetsuit. And my surfboard fit inside no problemo.

LawrenceS - My bad that I had read your thorough description in the sc430 thread but was seeing so many "how to” videos and explanations that ignored the method to keep the connection via the meter after the devices have all gone to sleep… So little did I know the one clear, sensible and unique explanation by you was the one that was gold. Had I really let it sink in and followed it, this whole thread wouldn’t have been necessary. So again, thanks!


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## LawrenceS (Oct 21, 2020)

richapple said:


> Holy cow, the bright light popped on above my head (did anyone’s screen brighten upon seeing this comment?) and not only do I finally “get it” now (thanks LawrenceS The Certified Honda and Hybrid Tech Guy), but now all is successfully resolved.
> 
> The 2019 Subaru Crosstrek Hybrid does have its 12V right up under the hood, entirely accessible, so yes, the loosened ground cable still making contact and allowing time to let the car lullaby itself to sleep did come in at… just the .03 Amps draw, bouncing to .04 a bit. 30 to 40 Milliamps, which explains the battery never really suffering. (Well, suffering a bit because I disconnected and charged way too often, and I’m sure that’s not good for a battery.)
> 
> ...


Glad something I wrote was able to help you. Also certifications don't mean ****, most of what I know was learned before I was "Certified" and I work with "Certified" techs who are useless, but since someone decided to question my qualifications I figured I'd back up my knowledge with my credentials(as if my avatar wasn't my, ASE Master Tech, ASE L1 Advanced Specialist and Honda Master Tech toolbox medallions). I'm just a guy who fixes cars for a living and I'd like to think I'm fairly good at my job.

The bounce in amps is probably from some flashing LED indicating the security system is armed. Lead Acid Batteries are designed to handle charging, on a normal vehicle they are charging every time you drive. Typically the biggest drain on a battery is starting the vehicle and then driving it recharges it. Being a hybrid there isn't as much of a drain starting it as it only has to power a computer controlling the big battery/electric motor, also as that other guy had said, the low voltage battery is charged by DC-DC converter from the big battery, so there may be slightly different charging logic as it is computer controlled not constant like from an alternator. Well new Honda's also use computer controlled alternators to reduce engine load if the battery's state of charge is high as determined by a battery sensor, more then once I've seen an independent shop replace an alternator charging at 12.6v because they thought it was bad but really it was functioning as designed.

As for the battery swinging low could be a couple variables, vehicles are typically designed to be driven fairly regularly and for a moderate distance to recharge the battery after the starting drain. If the vehicle sits for several days at a time and is only driven a small distance the battery may consistently be in a weak state making it more susceptible to a no start condition. Also taking the vehicle in for service can put a strain on a battery as the vehicle will probably be started and shut off multiple times without much driving to recharge the battery, from the service drive to being parked, from the parking spot to the bay, from the bay back to a parking spot, from that parking spot to a pickup area. So combine a discharged battery, with multiple short trips and then sitting for several days after might have just pushed it past it's ability to start the vehicle. Also the ignition may have been left on while in for service for any number of reasons, doing a lighting check/walk around, checking the car with a computer, performing an update and more often then not if a tech does have to leave the ignition on for whatever reason they are not hooking up a charger.

Also don't sweat it to hard about not getting my post first time around. Being a tech it's hard to think like an average person, while I try keep it simple I probably worded things in ways that don't click right away. Plus with the internet it's super easy to get misinformation or conflicting opinions.


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## argile_tile (Aug 1, 2020)

You said your untrained. The answer is simple.

AT THE DEALERSHIP, ONLY TRAINED TECHNICIANS ARE ALLOWED TO PLAY WITH THE ELECTRICAL ON ELECTRIC VEHICLES which they are allowed to do only after passing company courses on hybrid electrical dangers.

Even on oil changes the "lowly techs" are warned there are components they aren't allowed to touch and they must stay away from.

---------------------------------

If you have a Hybrid don't play with anything electric, don't mess with any of the wiring.

There is a big battery in that thing and it packs way more than necessary to fry you instantly dead. (and I don't mean the 12v battery i mean the hybrid battery)


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## LawrenceS (Oct 21, 2020)

argile_tile said:


> You said your untrained. The answer is simple.
> 
> AT THE DEALERSHIP, ONLY TRAINED TECHNICIANS ARE ALLOWED TO PLAY WITH THE ELECTRICAL ON ELECTRIC VEHICLES which they are allowed to do only after passing company courses on hybrid electrical dangers.
> 
> ...


It's still just a car and the basic electrical is still just basic electrical. All of the high voltage wiring is pretty obvious as it's covered in bright orange(or blue for the lower voltage systems on domestics I think).

So there isn't really an issue with him testing the electrical system as long as he isn't disconnecting bright orange things.

Even then I'm pretty sure most manufacturers also use some form of relay to power down hybrid systems with the ignition off for situations like car accidents where hybrid wiring may get damaged and could energize the chassis. Though if you are disconnecting hybrid components it is still required to manually shut off the big battery(they have built in switches) just in case.

And yes this is coming from a Hybrid certified dealer tech.


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## quatsch (Feb 4, 2021)

I'd think these large batteries could vaporize a dropped wrench.


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## de-nagorg (Feb 23, 2014)

quatsch said:


> I'd think these large batteries could vaporize a dropped wrench.



I know that I WOULD NOT be reaching for it.

ED


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