Battery Temp

glad you made it home in one piece. funny when you get that 100LB block of very dense material really cold, just how long it takes to start warming up. I do, like you, think that it is a real contributor to poor winter fuel economy. It doesn't want to contribute a lot to the energy required to move the car and it doesn't want any either. So only the ICE and MG1 to provide most of the motive power for the car. What was the final temp when you got home after your trip? do you remember?

 

ew, yeah, if i had to drive in those kinds of conditions again FE would be my last priority if anyone i cared about was in the car. glad you all got home okay.

that is an interesting observation, and supports what many of us have been hypothesizing. (there i go talkin' like some scientist again :lol: ) sounds like the battery really doesn't want to do anything when it's that cold. i can't imagine how long it would take, then, for the battery to fully warm up.

 

i have noticed low batt temps this past week also when we had our cold snap (probably the same one Evan experienced... just now getting to tail end of this one.) but i would go all the way to work and batt temps would never hit 40º. car warms up quickly still, but battery temps low and max charge and discharge is also low until batt temps hit at least 45º

 

i have noticed low batt temps this past week also when we had our cold snap (probably the same one Evan experienced... just now getting to tail end of this one.) but i would go all the way to work and batt temps would never hit 40º. car warms up quickly still, but battery temps low and max charge and discharge is also low until batt temps hit at least 45º

 

Interesting thought. Most battery chemistries do show a marked decline in capacity in cold temps, as anybody that's tried to start a car on a -20 Minnesota winter morning (even more so for a Jayman -40 morning), while thick oil contributes a lot, that old lead acid battery is down to about 50% capacity at best.

The thing that is puzzeling however is the indicated state of charge. I've never placed a voltmeter on the old lead acid, nor have I taken other NiMH for a serious cold soak to see how they fair. But the Prius shows a high SOC when I power it up in the cold, even after an all day sub-zero soak.

One theory however, perhaps the diminished cold weather capacity may be related not to partial discharge (lower open circuit voltage). Rather, it could be due to an effectively higher internal resistance caused by a slowed down electrolyte activity due to the cold. Same potential voltage but a much reduced current (amps) flow.

Just a theory on my part, maybe we could get a specialist in battery chemistry to chime in on this...

 

a normally fully charged lead acid battery's weak cranking power in cold weather verses a traction battery that is

1) never at full charge

2) rarely putting out power at that high a level comparatively speaking

is simply two different ball games. i think colder weather kills the mileage, but i dont think the traction battery's ability to charge and discharge plays that great a role. my stats show a pretty linear change in the mileage as it varies with temperatures. so no real evidence yet of cold temps and any major changes in charging. unfortunately, i have limited data since we only see sub-freezing weather at best a few weeks a year.

 

I think your probably correct or at least on the right track. A battery that has high internal resistance for any reason reaches a high state of charge relatively quick. As a sulfated battery will not crank an engine but will show a sp gravity of 12.75 or higher but has no capacity to provide amps.

 

So does any of this suggest that a traction battery heater as well as a block heater make sense???

 

I have noticed the same.. takes forever to warm up.. sometimes it does not fully warm up at all..
I can increase the battery temp more rapidily in heavy stop and go traffic..
It needs the charging to warm up..

Scott

 

My cabin heater does help with the battery. Not why I use it but it is a free benefit.
It doesn't warm it directly but starting out with cabin warm starts the battery warming earlier. My timers are set so the block heater goes for about 3 hrs and the cabin heater for 20 minutes.

In really cold weather I still don't count on much battery useage till I've been driving for 30 minutes. And you have to have set your engine up to get warm so you have heat at a higher fan speed to feed heat to the battery.

Toyota goofed again providing cooling for summer, but no direct temperature control for winter for the battery. I don't think they expected to sell so many outside of CA.
Hopefully they will fix these winter problems for the 2008 or 9 model. I assume Lithium cells won't really care if they are cold!

 

i guess before we decide that Toyota dropped the ball (not the first time we made that erroneous conclusion) maybe we need to determine just what the penalty is for a cold battery.

i for one, have not seen any issues related to cold weather operation. i feel that the reason my traction battery does not heat up is because i dont use heat that much. i guess i could try going places without a coat for a week or two, blast the heat and see if that makes a difference.

but considering, i am getting 50 mpg with below freezing temps, i dont think im being penalized at all. maybe Toyota isnt as stupid as we think they are.

 

took the wifes car to the gas station last night, first time I've driven it in a week and a half and was looking at the formatted screen and noticed that the charge and discharge rates were quite low 80 charge and 90 discharge, and it's been cold here as well as it's been in the south sound. After my trip to the gas station and back the battery was still only at 17C which is about 61F for 25 minutes of operation still very cold. OAT was 4C about 35F. It only really wanted to go into stealth readily about 5 blocks from home. I really should block off the rad in that thing.

 

its also kinda of funny that this battery thing only came up because of CANVIEW and CANVIEW only measures the "worst case cell"... now would that be the hottest cell?? or would that be the coldest cell in winter and hottest in summer??.. maybe the battery is much colder than we realize.

does anyone know what the freezing point is for the electrolyte? or does it even have that kind of stuff in it?? i have a ton of NiMH batteries for my RC car and none appear to have liquid in them.

now heat is a catalyst for all reactions, so that makes me wonder, if heat is bad for the longevity of a battery, maybe we dont want the complete reaction because it cant be reversed which would cause the battery to lose recharge capacity eventually killing it. so maybe cold is where its at.

granted IC's work completely different but i do know that the cold temp limit is nearly non-existent.

all in all, i think we be making much ado about nothing

 

The penalty is severe and can be as much as 20 mpg. However if you drive highway at 50 mph or greater, and don't have to stop for 20 traffic lights, it should have negligible effect on your mpg.

 

I read somewhere that the battery temp was an average of 6 sensors buried in the battery pack. On the Classic there are 4 sensors in the battery and 1 sensor measuring the temp of the air leaving the battery compartement.
Edit:
I've watched the 4 battery temps and have never notice more than a few degrees difference between them. I think that what they are looking for is if an area of the battery does get hot it'll signal the computer probably to set a code and possibly indicate a problem with some cells in that area. Speculation at this time as you can't get any confirmation on any of this stuff from Toyota.

 

It is absolutely correct that the battery cannot handle high currents
when it's cold. In the few times it's been frigid enough this
winter I've seen the pack refuse to either take or deliver any
more than 40 amps for quite a while, until it self-warms and/or
enough cabin heat drifts into the seat duct to help out. Gradually
the current limit begins to rise, but it can easily take over a
half-hour's worth of driving. That all depends on the type of
driving you're doing -- if you get right out on an interstate and
start steady-state cruising, there is very little current into or
out of the battery once it's up to 60% SOC anyways, so it is more
likely to stay cold. Self-heating is probably a more profound
effect than cabin heat infiltration, unless you're really blasting
the heat. And that's assuming you've got the heat on "fresh air"
mode, so the net flow through the car helps air get through the
battery pack and then out the exit duct in the back -- if you keep
it on "recirc", battery airflow will probably be less.
.
What this mostly affects in driving is probably regenerative-braking
capability. If you can only shove 40 amps in as opposed to the
warmed-up 100 amps, the system will fall through to physical,
energy-losing brakes much more readily, and now you're losing
all kinds of energy off the wheels. So in stop-n-go traffic,
that probably represents a notable loss while the battery is still
cold. On the highway it's probably less significant, but now
you've got air resistance, pushing slush out of the way, etc etc.
.
Observations from people tend to indicate that the system does try
to deliberately work the battery a *little* harder when it's cold,
such as by running the SOC a little higher which is why green bars
are seen more often in the winter. But if the type of driving
you go do at the time doesn't really allow for that, you just lose.
.
_H*

 

The battery temps have been off my radar but I am starting to watch them. Our mild climate will make collecting data harder. I started out at 50 this am with an outside temp at 49, it went up to 61 at the end of the trip. I guess there may be an argument for slowly increasing the cabin temp after you reach and stabilize the car in full hybrid mode. If you wanted to pre heat a battery it seems to me that it would be easy to use one of those small space heaters, I have one that is a cube about 6-8 in and attach a dryer exhaust hose to it and run that to the battery in vent set the thermostat and leave it on for the night.

 

Hypothesis: If you ensure the battery is drained (using EV mode) the night before, then during engine warm-up, it will get charged. Will this initial charging significantly raise the battery temperature, thus leading to a net increase in efficiency?

 

It's the nature of batteries, they love it when it's warm, hate it when it's cold.

What surprises me is that Toyota didn't attempt to warm the battery compartment. Heck, from what you say, just a simple diversion of cabin air could've helped a lot.

Glad that poor gas mileage was your only problem running in those conditions. Ice and snow driving can get pretty nasty at times. Glad you made it okay.