Traction Battery loses charge overnight

I haven't noticed anything like this but I don't closely monitor my HV battery's SoC. I will say that for the previous night, after sitting overnight, per SG, I didn't lose any HV battery SoC.

As for your 12 volt being original, it's very likely it needs replacement by now.

 

You could use Torque app with custom PIDs to pinpoint which module is the cause. There maybe a weak cell in that module.

 

change your 12v battery.. it's about to die.. or find the post that explains how to add water back into the cells to make it "re-built"

clean your HV fan if you haven't.. mine was caked up a good 50% with just dust (in my mind that's a failed fan)

temp dropping is either bad cells as mentioned above or a heat issue where the battery cools and the voltage drops.

 

Yup, replace the 12v battery.

 

There are 2 separate low HV battery problem here.

If it is +/- 1 bar from where it was when you parked immediately after turning on, then it drops like a rock, it is more than likely your 12v battery. A bad/dead/dying 12v looks like a giant load, and pulls a large amount of current from the inverter to charge back up.

If as soon as you turn it on it is at 1-2bars and was at 7 bars when you turned it off, then you probably have a weak HV battery cell.

When the car is not READY, the HV battery is 100% physically disconnected from the car. (It uses relays to connect only when READY) So if it drops with no external stimulus, then the problem is internal. If you have a weak cell, then all the other parallel cells are going to "charge" that cell. Batteries in parallel must be 100% equal potential for no current to flow. Obviously this is impossible for anything outside of a laboratory and even more so with aging as chemically they will be different after different time, use, temperature, physical stress and so on. So the amount that they are different by and trying to recharge eachother is what contributes to the "self discharge" rate. They are discharging into eachother to keep everything as balanced as can be. If one cell is lower than the others, it will take charge from the others. If it is a bad cell and cannot be fully charged for some reason then the other cells will constantly be "charging" it which is an exercise in futility and will just drain the pack.

 

I drive a 2005 Prius and am having a similar issue with the HV battery discharging overnight (or overday, while at work); however, it is inconsistent. One time it will lose no or one bar, but another time it may lose five bars, so that it only has two bars left, the bars turning red. I recently replaced the 12v (with an Optima Yellow top), so that should not be an issue. I just noticed that the key indicator light flashes on and off constantly after I turn the car off and leave. I tried putting the key in the most distant place in the house, but the car's indicator light still flashes. I should mention the car has well over 300,000 miles and I replaced the engine and transmission 10,000 miles ago, (a used set with 70,ooo miles thanks to Steve at autobeyours.com). When I drive the car on back roads, I average 60 MPG, even starting out with the handicap of a low HV battery (mine also recharges quickly).

I have been considering installing a plug-in conversion kit, which includes a lithium battery pack. I assume a bad HV battery could ruin the whole project.

Should I test the HV battery for bad cells? If so, how?

 

Sounds like the remote is damaged. Very common problem. The rubber cover over the keys gets chewed up and push constantly on a button. Look at the remote closely. That's really hard on the new 12 volt battery. Lets sort that out first. A bad 12 volt battery hammers the Hybrid battery.
Get dc volt meter and first thing in the am without starting the car measure dc across the jump points under the hood in the black plastic fuse box. Write that down. Then get in car and without pushing the brake push the start button once....then again. 2 pushes. Its now in IG mode and the engine will not start but there's a load on the 12 volt battery. Get out of the car and measure the dc again. When done just push the start button with brake on and car will start. Shut it off.

Report those 2 numbers back here.

 

I have read through a number of posts discussing HV/traction battery charge loss. My wife's 2008 Prius (55000) recently has been having frank power loss. The reproducible part of the problem seems to revolve around the HV SoC dropping rapidly (within 1/2 to 3/4 mile) to 1 to 2 bars after she fills her tank and begins the 2.5 mile trek home which is a relatively gentle up slope the entire way. The gas motor seems to be running constantly (certainly much more often than before this power phenomenon began) and mpg is somewhat less than previously enjoyed. We live at 7200 ft and she drives to work down to 6400 ft over a distance of 20 miles or so (about half at highway speed and the other in-town traffic). SoC indicator has gotten as high as 6 to 7 bars going into town and upon return home drops rapidly from 6 to 7 to 2 to 4 with the upgrade. Previously, SoC would be 9 into town and no lower than 5 to 6 if I really pushed the speed coming home uphill. We have taken the car to the dealer who has told us to drive in B mode as much as possible, followed by we are not driving it enough (without qualifier of just how much driving it needs to be "enough") to comments from data pulled from the memory saying we drive with brake and accelerator at the same time to driving before the "ready" light is on. It has had 2 bad 12 volt batteries which were replaced well before anything we are experiencing now and the current battery checks out each time we bring it in. I believe the main HV battery is beginning to go bad but the dealer and the "experienced" Prius tech say the above reasons. I am going nuts. Anyone have more insight for me?

 

welcome to priuschat! might your 12v need replacing? you might have a parasitic drain on it that is requiring constant recharging and eventual early death. i wouldn't trust them to 'check it out'. especially from people who told you to drive it more or use 'b' mode more or you're driving before the ready light comes on. none of those things would affect it. i have to ask tho, does one of you drive with two feet? that's a no-no.

 

I noticed that when its cold out (below 45*f), my HV battery on my 2007 loses a bar or two overnight. Today when I got into the car, I had 2 purple bars (the lowest two) but last night before I parked it I know I was somewhere in mid-range, in the blue bars section.

My 12v battery is brand new as of last week and reads ~12.75v resting. Its not that...

 

Hi dermguy. Mountains do give the HV battery a workout, so you may find the your traction battery doesn't last as long as it should.

Can you clarify a few things about your post.

1. You seem to indicate the problem only happens after she fills her gas tank, but I suspect it has nothing to do with the gas tank or the act of filling it. Normally this type of thing happens during the first few minutes of driving while the engine is still cold.

2. You state some information about the number of bars of SOC (state of charge) but I am not sure how accurate are your observations. In particular you mention "an SOC of 9", but it only goes up to a maximum of 8. So just to summarize, 1 and 2 bars display as red (or purple), 3 4 5 and 6 bars display as blue, and 7 and 8 bars display as green.

 

About 6 months ago I replaced the AUX battery with an Optima Yellow Top. Since then I have noticed that on occasion the HV Battery SoC will drop from Max Blue Bars to two Red Bars over a period of about an hour. I noticed this because I will often set in the car at a local marina or elsewhere and read. Yes, I do leave the radio on but the car is in ACC mode which should have the HV battery disconnected from any load. I have not had any problem starting when this happens and the SoC quickly recovers to Max Blue Bars after a short drive.

I have not observed this happening overnight when I park the car in the garage.

I'm really wondering if this may have something to do with ambient temperature. While the windows of the car are open the rear deck does become hot from the sun. Also, in one specific location the rear of the car is located near a large power transformer. Is there some kind of EMF causing a problem in the HV battery controller?

I have taken the time to monitor the 12VDC batter (using the MFD) and don't see anything unusual even if I place the 12VDC battery under the load of lighting the HID headlamps.

This is really a puzzle to me and I hope that someone will have some ideas. Since I cannot dependably duplicate what is happening I cannot simply take it to the dealer.

Thanks.

 

I like books on tape (well, CD these days). One time I was working near the car and left on playing in the ACC mode. It could possibly have been the "no-brake" ON mode. What I do remember is that I lost SoC bars rather quickly. I think that Prius does not like to serve as a boom box.

 

If you leave the car in "ON" then the traction battery is connected and the inverter is running. Also, the AC is running so you can lose SoC rather quickly. However, in ACC mode the onlything that should be providing "amps" is the 12VDC battery so unless there is some relationship to the SoC of the 12VDC battery and the indication of the SoC of the traction battery the SoC on the MFD shouldn't change.

 

There is an exact relationship between the Hybrid & aux battery. If you pull the aux battery low sitting there in ACC The second you turn the car back on that low aux battery load is the biggest load the Inverter see's. And the Inverter uses the Hybrid battery as its power. the Inverter is doing all it can to charge the aux battery back up and pulls a large instantaneous draw on the hybrid battery to do it. This happens very fast and happens before the mfd comes online so you don't see the hybrid battery soc drop. So it looks like the hybrid battery soc has dropped before you started the car. Like its lost its soc just sitting there.

I have seen many posts about sitting there reading in acc. You are not saving any gas and all your doing is stressing the aux battery. The gas you think your saving will be quickly used to recharge the hybrid battery that was just slammed to recharge the aux.
Leave the car in READY if your sitting there. It will use very little gas and be more thrifty in the long run.

 

Thanks for the explanation. I'm not really expecting to save gas. I just don't see any reason to have the ICE start/stop as it does a short top-off of the traction battery when the SoC gets low. Especially since the top-off cycle is fairly short and doesn't really top the SoC off but only pushes it about 2 bars blue. Next time I will try leaving the car in the "ON" mode (AC Off) to get a feeling for how fast the traction battery SoC drops.

Thanks again. The thing that had me concerned was that sometimes the SoC on the traction battery drops to 2 bars while at other times it will hardly drop at all even when the "Park" time is about the same (1 hour).

 

Whats the problem with the ICE coming on and off? That's not hurting anything. And it won't "top it off" but will keep it from getting deeply discharged.

And to your second concern it all depends how much soc is to begin with.