sudden battery discharge

I have a 2005 Prius, purchased new in 12/05. I live where the temperature is warm/hot most of the year.
Some months ago, I began having a problem with the battery suddenly discharging to one or two bars while I was waiting at a traffic light. This does no occur as a gradual decline in the number of bars on the display, but happens suddenly and is accompanied by an engaging of the gasoline engine which seems to be somewhat "reved" up.) (I do have the air conditioning running due to our weather here.) This has been happening with increasing frequency. I have taken the car to the dealer four times and have been told that there is nothing wrong with the car. My gas mileage has gone from an average of 43 to 44 mpg to 28 to 31 mpg. (After the sudden discharge, the mileage is really poor until the battery regains its charge.
I'd appreciate your thoughts and experience. Please help!
EJ

Hi Elizabeth,

Please provide a few more details:

• Odometer reading
• When the traction battery SOC gauge drops down suddenly to two bars, what level had it previously been at
• Does the SOC jump back up or is it very slow to rise back up to 5-6 blue bars
• How is the terrain where you live - is it basically flat or do you have lots of hills and valleys to go up & down
• How often does this happen

I assume that you don't have any warning lights on. Its unlikely that the dealer will take any action until that happens.

If you see the SOC gauge rapidly moving up and down, I would say that this is early warning of a pending traction battery failure.

Thank you for your response. Odometer reads 46,200 miles. The meter usually shows 5 or 6 blue bars before dropping suddenly to 2 (& occasionally 1). It takes a couple of miles for the monitor to show 4 or 5 bars again, a bit more for 6. The terrain is flat, the climate is hot (South Florida). Sometimes it occurs several times a day, occasionally there is a glitch-free day. This past Thursday, it happened 4 times, Friday, twice, today, only once. I have no warning lights and the dealer says that the computer shows no error codes, therefore, he says, nothing is wrong with the car!

Hi Elizabeth,

Thanks for the additional detail. Does the traction battery SOC gauge rise from 2 to 3 to 4 to 5 bars over time; or does it jump up from 2 to 5 bars?

Make sure you are holding your foot on the brake pedal hard enough while stopped that there are no lines showing on the energy screen. If you only have light pressure on the pedal there is energy being used to try to move forward. This isn't likely to be enough to account for the sudden drop but may contribute.

The recharging from 2 to 5 bars takes some time. It occurs over 2 or 3 miles, and is not an instant recharge. Thanks

Thank you for your response. I think my foot is firm on the pedal, but I'll watch the screen to be sure.

how long are you waiting at the traffic light?

how fast does it drop down from 5-6 bars?

How low is the AC set?

I'm seeing a troubling hot weather battery related low MPG complaint trend here. 3 different threads started in the last few days:

http://priuschat.com/forums/prius-main-forum/48675-sudden-battery-discharge.html

http://priuschat.com/forums/care-ma...d-hv-battery-drain-startup-hot-days-only.html

http://priuschat.com/forums/fuel-economy/48662-drop-performance-mpg-going-dealer-please-help.html

I'm thinking this could be a widespread "defect" in Gen-II Prii...

The AC works as hard as it needs to to control the temperature, if it is very hot outside the compressor will run at full speed and the fan runs fast to lower the inside temperature. This can drain the battery quickly at traffic lights. You don't get anything for nothing so if the AC is working hard it will impact on economy. I'm not sure this is a factor here but could be worth considering. I generaly set my AC to 24 degrees C and let the climate control do the thinking. I do get a 0.3 to 0.5L/100km hit in summer from AC use but I normally only need the AC for half of my commute as I either start work before it gets hot or finish after sunset so I drive most of my journey below 70km/h with the window down in summer when it's cool enough. If you do all your commuting during daylight you may get a bigger hit than I do. My commute is 35km each way and takes about an hour. The most important thing with AC fuel consumption is time and temperature rather than distance, the slower traffic moves the bigger the MPG hit.

Set your A/C and leave it at 77

#2 is normal Prius behavior. If you start the car and immediately flog it, the battery will drain extremely quickly since it does most of the work until the engine has warmed for 30-60s. The impact is especially pronounced when the A/C is running since the drain is that much faster. (I take it very easy out of the drive/parking lot to avoid this.) #3 sounds like a combination of hot weather (CA) and new, non-low-RR tires. Also normal Prius stuff.

#1 (this thread) sounds like something different. A step change from 5 or 6 bars to 1 or 2 is not normal and I would suspect a problem with the HV battery or the battery control module. Fortunately, at 47,000mi there should be plenty of life left in the warranty! A trip to a **good** dealer might be in order to check for signs of degradation (uneven voltages between sub-packs.) However it's a given that they won't replace anything until it throws a master warning light and a code.

Traffic lights vary, but probably average 1 to 1.5 minutes. The drop from 5 or 6 bars occurs in a flash. The AC is set for 75 degrees. Thanks for the reply. I hope you have some ideas.

Thank you for noting the cluster of mpg/hot weather issues. I am new to the forum and am probably not using it as efficiently as possible. Do you have any ideas as to how to get help with the problem? The dealership, after 4 visits, insists there is nothing wrong with the car because it shows no computer "codes". I'm getting 28 mpg on my current tank of gas!

Thanks for the response. The summer temperatures in South Florida are hot and humid! Morning temperatures reach the upper 80s and afternoons are frequently in the 90s. The AC is a necessity. I keep the temperature set at 75 degrees. (Dorry, but I can't make the temperature conversions- how warm is 24degrees?)

Easy way
24 plus 24 is 48, 10% of 48 is 5.....so 48 minus 5 is 43 plus 32 is 75F

Hi Elizabeth,

It looks like you are driving 15K miles per year, so your car has been getting good use. However, has your commute pattern changed where you now are driving much shorter trips than in the past?

Your observation that the ICE is running much more than in the past is the reason why your mpg is so bad.

I think that your car is a very good candidate to get a new traction battery under warranty in the near future. You might try taking it to another dealer to see whether they can measure individual battery module voltages and discern any problems. However, as was previously pointed out, it is unlikely that any repair action will be taken until your dashboard lights up like a Christmas tree.

When your car gets to the point where the SOC gauge moves up as quickly as it moves down, then hopefully the hybrid vehicle warning icon in the MFD will appear, and you can get your new battery.

Easier way: use one of the Internet temperature calculators:
Temperature conversion between degrees C and F

If C is the Centigrade temp and you want to convert to the Fahrenheit temp F, then the formula is ( 9/5 x C ) + 32 = F

0. Did you recently buy new tires or get the oil changed?
1. What are the pressures in each of the tires right now?
2. What is the level of oil on the dipstick?

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