Do drive motor batteries drain overnight?

no, you have a serious problem if you are not mistaken. what kind of mpg's are you getting?

 

45-50 is pretty common around here, but over 50 is certainly achievable if you drive correctly and there is nothing wrong with your car. read thru some of the newbe threads here and tips for better mileage. 2 things tho, your battery should not be full every time you get home and it should not be empty every morning. i would schedule a trip to the dealer.

 

Does the HV battery show a low state of charge IMMEDIATELY when you turn the car on or does the HV battery drain down after a few hundred yards?

If you park the car up with a full HV charge and it is down to low the next morning when you turn the car on then you need to get the car checked out.

If the car starts with the same charge from the night before but quickly reduces then this is what my car does and is normal. Apparantly the car will try to let the engine warm up smoothly for emission purposes and does this by using the HV battery to propel the vehicle with the engine running at a constant revs. Once warmed up past a certain parameter the car then reverts to charging the HV battery as well as warming up.

It seems to do this in the first warm up cycle and only if you're very light on the gas. If you hit the red power band it seems to stop this particular cycle.

I'm sure others will confirm the exact reasons or tell me I'm completely wrong.

 

I will address the mileage issue. You did not indicate total miles driven, so I'm thinking that your ICE is not fully broken-in, especially since you have no highway miles. My guess is that as you get more familiar with the car and possibly add a few more miles, your mph will go up.

 

I have never seen my SOC vary more than one, possibly two bars from night to morning. I have had my Prius coming up on two years now.

Do you drive with your headlights on all the time?

 

One thing that is curious about your first post is that you say your battery is fully charged at the end of each day. Unless the last 5 miles of your daily drive is at the bottom of a really steep hill, your battery won't be fully charged at the end of the day. FYI, I've never noticed any loss of charge overnight, so if this is real, get it checked out by the dealer.

 

Check the number of bars just before you shut the car off, then check again when you first start it up. It shouldn't loose more than one, usually none. When the power is off (ready light off) the HV battery is no longer connected to the car and it should retain it's charge for months.

Here is another thread on the same topic
http://priuschat.com/forums/gen-iii...799-battery-charge-down-4-bars-overnight.html
Unfortunately the OP on that thread didn't report back with what the dealer told him, at least not yet.

 

Did you leave the car turned on?

 

Yes it does but you have got to go down a really long steep hill for it to happen.

 

I've been away on vacation a few times for about a week and the HV battery level stays the same.
It will be rare that you get full charge (up to the two nubs). I have seen it full charge on 2-3 occasions in the last two years. (going downhill or coming off a highway which has a slight downgrade.
Did you add any after market equipment, alarm system, keyless start, stereo, lojack etc...?
I would have the dealer look at it.

 

Yes it will under some circumstances as mentioned by TheSpoils. It is designed to run with 3 to 6 bars most of the time, it will rarely use the bottom two, in fact I have only seen it use one of those one time in 37K miles. The top two will be used to store extra energy from regeneration so it leaves them for that purpose and you will see them used when coming down a long step hill for example.

I think your service representative is incorrect on that point, if a battery drops overnight by a bar or two it would be because of temperature change. There is no way the car does this to itself to preserve the battery or for any other reason. When the car is off the battery is disconnected, no more energy in or out.

 

Do you have remote start? have you triggered it accidentally?

If it's genuinely gone from 6 bars to 2 bars overnight then either the car has a serious fault, or you left it switched on.

Do you park in a garage? do you lock the car when parked?

 

As it looks like nobody really have a clue why this can happen, I can try...
Battery voltage (and as a result SOC, and bars on the MFD) changes with temperature. Batteries are warm and charged after driving and show high voltage that results in all full bars on MFD.
When they sit overnight, they cool down significantly, and voltage drops. Then you turn the car on and you see less bars (calculated form less voltage measured by computer). This effect will vary as at different locations temperature change will be different. Also the temperature of the "hot" battery depends on how intensively it was used just before the shutdown. That's why many people don't see a SOC (state of charge) drop in the morning.
I do see similar behavior in my 2005 with 117 k mi. The car drives fine, gas mileage is good.

Best, Alex

 

Nope, SOC is calculated by counting amps in and out of the battery, not by it's present voltage. If you did that you'd see wild swings while driving, since anything between 180V and 250V is perfectly normal.

 

Flaninacupboard, It could be done the way you said, but then there is no way SOC would show different values (before shutdown vs. after start) as there would be no accounted in/out currents when car is turned off, only last recorded integral value.
This method (summing in/out currents) could be used only for short time intervals while driving (to avoid surface charge effect, etc).
I see significant drawbacks when using in/out currents for calculating SOC over long periods of time

Thanks,
- Alex

 

SOC can be recalculated on restart if 12V has been lost or voltage seems at a strange value.

You're correct that reported SOC -shouldn't- change between shutdown and restart, since no power goes in or out of the battery and real SOC doesn't change.

 

bet yours doesn't loose charge overnight? cos its plugged in!