View Full Version : Battery Losing Charge
03-19-2007, 12:45 PM
Wasn't too sure where to post this, so bare with me if it's in the wrong section. The past few days I've noticed that my battery has been losing some charge when it's been turned off. I'm on an '02 Prius so my FCD only shows 3 levels for the battery. My battery is usually on the highest level when I turn the car off, but the last few days when I've turned the car back on, like the next day, it'll be on the second level and it'll take about 5 minutes for the battery to go back up to the top level.
Before you go saying it's an old battery, just know that the battery was replaced 2 years after the car was bought. In other words changed in '04.
Also, today it seemed like I wasn't having the problem, but today was about 25F warmer than the days where I did lose a lot of charge overnight.
Any ideas on what is causing this?
03-19-2007, 01:12 PM
The obvious thing to watch for is anything draining the battery. If you have a multimeter you can test directly on the 12V battery's leads and watch it for a few minutes. If you see it dropping so much as a few hundredths of a volt over a few minutes while the vehicle is off then something is draining it.
03-19-2007, 01:25 PM
Are we talking about the high voltage battery or the 12V? The mention of the FCD sounds like it's the HV?
Have you been monitoring SoC throughout the life of your car? Never happened before?
Not to dismiss your claims, but I see the same thing in the '07 and I've given blame to temperature. If you look at my weekly logs, you'll see a few times where the Start_SoC is lower than the Previous End_SoC on my weekly trip reports (start in my sig and work back).
I've heard that the battery is terribly ineffective cold, so I assumed that a battery level that was read at 75F, then disconnected, and stuck in a freezer for an hour, would come out (at 35F) reading a slightly lower level (because of the temp delta).
So I wrote it off to my car cooling overnight.
I also check the SoC before I boot the car (at IG-ON). I've seen SoC drop due to the 5 secs of EV mode Reverse that the ECU allows me.
I've also noticed (Prius II again here), that simply having the car "booted" consumes a lot more energy that I would have initially thought.
Example: Park your car, turn off all electronics and the display, leave it in Park but don't turn it off, then walk away for about 20 minutes. When you come back you should notice that Those 20 minutes consumed (on a Prius II) 2-3 bars of SoC.
___If it is the HV pack, SoC via the mimic can show all kinds of things not entirely based in reality. Measuring the terminals over time while parked and dead will give you a better idea if there was a leak path but I highly doubt you have a short developing. There have to be quite a few redundant protections for that not to throw some kind of CEL?
___Did you state you had the HV pack replaced or did you mean the 12V? I have heard of just a handful of Prius I/II packs replaced and most had to do with accidents. I don’t think I could count on one hand the number replaced for a defect although I do not follow the Prius groups like I should :(
03-19-2007, 08:01 PM
I'm not entirely sure, I believe it's the HV battery. The owner before me had it replaced so I don't know what the circumstances were.
It seemed to happen again today, but while I had the car running. It's hard to know for sure since I wasn't watching the screen very well.
03-19-2007, 09:30 PM
When you leave the car powered up for 20 mintes, you're
still drawing 350 - 400 watts to power all the electronics;
that's 130 or so watt-hours which is roughly a quarter of
the pack's apparent "capacity" as shown on the display.
Because of the SoC limiting, you only get about 600 wH to
play with total. So yeah, you'll see a drop. It is likely
still less energy than putting the engine through a whole
'nother catalytic warming cycle, though, so I tend to leave
the car powered up over short errands too.
All batteries have a certain self-discharge rate. Nature
of the beast. The NiMH cells in the Prius are pretty good
in that regard, i.e. their self-discharge is fairly low,
but still enough to notice over a long sit.
03-20-2007, 09:23 AM
Also, check the 12V battery for load. Your 12V could be getting bad and your DC/DC converter may be working overtime draining your HV battery. Check if the 12V battery has the stock part number to see if it was replaced instead of the HV battery. The owners manual should give you that info.
03-24-2007, 06:10 PM
Hobbit, so are you saying that you leave your key in the car while you do errands? Maybe not fully on, but in the on position? If I'm wrong then please let me know, because I hate having to go through another warm-up session when I have to dart into my apartment for like 2 minutes.
___Yes, leave it booted up so you don’t have to take the very short - simulated warm up hit even after it is already warm. Be careful though. Leaving it in a ready state and then forgetting that it’s still live in the drive or garage will have her cycling on and off again and again until she eventually runs out of gas in about a month or two ;) Or someone decides to take her for a joy ride without your permission. There are ways to lock her up while in a Ready State to avoid that problem too :)
03-25-2007, 01:18 PM
Yea, I guess I could always keep one of those extra keys on me. Hmmm, I'll have to look into it. I have the classic Prius, so I can't use the tricks I've read about on here.
So let me get this straight, I just leave it on, but like in Park mode? Or are you saying I turn the key back one click and then forward back to on, but not started?
Hobbit, so are you saying that you leave your key in the car while you do errands? Maybe not fully on, but in the on position? If I'm wrong then please let me know, because I hate having to go through another warm-up session when I have to dart into my apartment for like 2 minutes.You got it. I detailed how to leave your prius running on a Daily Grind post here. But like I said in the post, It consumes Wh to do so, and if the battery state gets too low, the engine will kick on.
03-25-2007, 06:23 PM
Oh, oop, I forgot to mention that I've hacked my Prius' fob slot
so that I can pull the fob out while the car is still
powered up. This is a reversible one-wire mod -- you extract
one of the blue retaining solenoid wires from the connector
in the back of the fob reader. If your car has smartkey, then
it doesn't matter since it's already out of the slot.
So what I do is have the fob on me, but not hanging on the
metal key part -- and as others have detailed, just get out
and lock the door with the metal key for quick errands. I
also often turn off the MFD backlight because that *does*
save a few measly watts on the 12V side. That electronics
load isn't exactly "phantom", when you consider it's about
300W baseline and you can feel heat on top of the MFD hump.
To answer Alexstarfire's question -- in the 3rd-gen Prius, there
aren't "positions" you click a key to. It's the "fob" style
that is also starting to show up in other cars, either held
somewhere inside the vehicle [smartkey, longer-range RF based]
or inserted in a passive-RFID reader slot [or in the case of
the Camry, just held up to a magic spot near the power switch].
There is a risk that someone could bust in and take a joyride,
but only until they powered down. The question often seems
to come up about taking the smartkey away from the car while
it's powered up -- people don't realize that no, sorry, it's
not a jacking alarm that will shut the thing down when its
key gets a certain distance away. The immobilizer check is
a one-shot thing when moving to IG-ON or READY mode.
03-27-2007, 12:28 AM
I guess you people keep skipping over the fact that I have a Classic Prius, not the new 3rd Gen Prius. I'll go take a look at that link you posted though.
03-27-2007, 09:40 AM
What they are talking about is cars with the keyless ignition. I think they did forget you have a clasic prius.
03-27-2007, 10:20 PM
Well, I figured out a way to do it, but it doesn't seem to help too much. I just did it a few minutes ago when I parked it for about 5 minutes each time, had 2 stops. My MPG was 63.9 at the start, and 64.1 at the end. It was a little over 45 minutes of driving. I didn't think that was too good considering it's been hovering around 64 MPG before I tried this.
Basically what I've done is leave the car on, put it in neutral, apply parking brake, turn lights off (if needed), turn screen off, turn off radio, leave car, etc..
I thought it would yield a much better result since I could use the battery a lot when I had to park, but that wasn't the case.
I'll keep trying it and see if it changes. I think that my car just uses up a lot more power than the newer version, but IDK.
"Put it in Neutral".... clever... never thought of that.
Disables the ICE starter right?
03-28-2007, 09:57 AM
Yep, cause putting it in park almost always makes the ICE start, regardless of your battery power.
You could leave it in drive, but then you'd waste battery power trying to move the car. Plus it wouldn't be too good if the brake failed.
03-28-2007, 07:19 PM
Okay, yes, enthusiasm got in the way of remembering that the
original problem statement was for a Classic. Well, hopefully
the li'l rant about what to do on a PII is still useful to some
folks. Anyways, for the classic ... all I can think of is,
how many physical keys do you have? I generally keep my keys
attached to me on a fairly short cord, which can't reach an
ignition lock, so in my other cars I would generally keep another
key somewhere *in* the vehicle in a little hidey-spot under
the dash and use that for starting it. I could leave it powered
up [which, back then, meant idling, bleh] and get out and open
other doors or whatever and still lock/unlock from my keyring.
So you could presumably do something like that in a Classic.
Look at http://priuscar.com/keyless_prius.htm for how another
guy rigged up his Classic. Almost like he invented his own
smartkey before the '04s came out.
I only wish the remote clicker would work with the car powered
up. I looked into hacking it but the mechanism that ignores
the RF receiver is buried deep in the body-ECU firmware so
there doesn't seem to be a handy input to just fake out.
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