04 HV Battery Question

[smithBYU85]

I have an 04 Prius with it's original HV battery and I'm wondering if it's starting to have some problems. I have NOT noticed a significant drop in MPG, it's where it's always been. What makes me wonder is the indicator on the MFD, the indicator stays around half-full and has stopped rising above that point. If it does, it's only by one bar. I believe dealers are able to check the battery, but is that worth it and would be covered under Toyota's extended warranty?

[hobbit]

What altitude do you live at?
.
_H*

[Flying White Dutchman]

you will almost never see full green
normally blue halfway
so i think its normal.

[smithBYU85]

Originally Posted by hobbit

What altitude do you live at?
.
_H*

I don't know the altitude, but right now I'm in Provo, Utah so I'm in the mountains.

Originally Posted by Flying White Dutchman

you will almost never see full green
normally blue halfway
so i think its normal.

I know it won't be green for long in the few times it actually gets there, but the indicated level is lower than it has always been. I don't know if I'm worrying about nothing, that's very possible. I don't know how accurate the MFD is about actual battery charge levels.

[Patrick Wong]

Hi T,

Since your mpg is holding constant, I would not worry about the battery at this time. Yes, you could have your Toyota dealer tech run a test on the battery but that would be at your expense, unless a warranted problem was found.

I live at 1,100 ft elevation and have found that my battery SOC gauge routinely will rise to seven or eight green bars upon descent to sealevel; however I think of this as an indication that the battery is losing capacity; hence the battery shows changes in charge/discharge level faster than normal.

[hobbit]

Okay, first of all, the HV battery gives you 600 watt-hours to
play with which happens to be, shown-empty to shown-full, good
for about 500 vertical feet of elevation if you get optimal
conversion in regen. That's keeping fairly low currents, which
may be impossible on some mountain highway descents since it requires
going fairly slowly sometimes. See this for details on when I was
able to do some testing under somewhat controlled conditions.
That's why you're topped out way before completing that 1200
foot descent.
.
Second -- when my own '04 was at 4000 or more feet of altitude,
I definitely noticed that the SOC stayed much lower than usual.
I have no idea why, especially since the car has no barometric
sensor in its control systems so how could it know? Nonetheless
it would continue giving assist and only level out around 4 bars
in the display rather than the normal 6.
.
When I went over Vail and Loveland passes in CO at 10,000 feet or
so, the car used up *all* of the available battery -- I'm talking
down to ONE bar in the display and still pushing arrows toward
the wheels, even with modest demand at the pedal. Unless I ran
the engine up to like 4000+ RPM, I couldn't climb particularly
fast since that was the only power source left. I was content
to just drop in behind a slow truck and wait it out through the
gorgeous scenery, since I'm not one who subscribes to the school
of thought where manhood is proven by how fast your smoke-belching
Powerstroke blasts uphill with the boat in tow, but it was still
somewhat puzzling why the car had gone out of its way to exhaust the
battery so soon in the game. The only change was altitude, and
things returned to the "new normal" 4 or 5 bars once back down to
5000 feet and then right back to 6 as I returned closer to sea level.
No codes, no complaints, just a clearly changed target SOC during
most of my westward wandering this summer.
.
The only guess I can make is with the engine having to pull in
more air to match burning enough fuel to get requested power,
and definitely keeping the throttle farther open as seen on my
vacuum gauge, that enough of a mismatch existed between the power
the hybrid system wanted and what it actually got from the engine
that it felt it necessary to make more up from the battery. But
that really should only be for transient situations, not steady-
state on the highway where I also had the low SOC the whole time.
.
I asked about this on Prius_Technical_Stuff and other people at
high altitudes reported NO changes from the normal six-bar 60%
SOC level. Different year cars, though, I think, suggesting a
possible change in ECU coding to handle this. I don't believe it
had anything to do with the occasional tank of 85 octane I was
getting in those areas, either.
.
_H*

[smithBYU85]

Your experience is very similar to mine. I'm in the Utah valley, so I don't do much driving up and down mountains. When I drove out here in late August I had the same trouble driving up some tall mountain passes. At one point I lost 15 mph coming up a pass and the battery was at 1 bar, just like yours. When I left for home in Illinois at the end of last semester, I climbed all mountain passes without even losing 1 mph. I'm slightly concerned, maybe I should have the battery checked after all. I just don't want to pay the cost....

[hobbit]

Another thing I'm wondering is if the decrease in ambient air
pressure has any effect on the battery cells. Since they're
pinched together with tension rods I wouldn't expect them to be
able to expand much, but who knows, there might still be some
physical effect on the interleaved plates. I would expect that if it
were to have any effect at all on the car, it would be one of current
limiting, not of where the SOC sits. I don't think any of this is a
*problem* with the battery per se, just some odd side-effect. And
different model years with the same battery type seem to be, uh,
"immune". Like I said, everything's right back to normal down near
sea level and I haven't seen any odd symptoms since early August
when I was out there.
.
_H*