12 volt battery

Hi Amanda,

If you drive six miles a day, I assume this means two trips, three miles each way. How many minutes does each trip require?

I would say that this well may be insufficient usage for the 12V auxiliary battery to remain charged up; proof of this is your dead battery incident in December.

I agree with Tom that once the car is READY, the DC/DC converter provides all 12V power to the various accessories. The heater can draw heavily on the 12V bus if the two PTC electric heaters are on.

However, if your car is not running long enough to keep the 12V battery charged, then you may have a repeat of the Dec. 29 incident.

If your schedule does not require longer trips at any point during the week, then you may want to invest in a battery minder to keep the 12V battery charged up and in good condition.

 

It is difficult to impossible to analyse anothers problem from sunny California, but I'll try. Because of the puny boot-up battery (12V) I make sure nothing is left on in the car by way of lights, in fact I do not use them (trunk, door, interior, etc.) if not needed I do not use the headlights, except where law prevails. One can check the strength of the bat with a multimeter, or failing that, the MFD gives you the option of checking 12V level both in Acc and ready mode. Hold Display, click headlights on and off 3 times, go to menu, display, signal check = 12 VDC level. Almost always something more than 12 (a bare min) usually 12.3-12.6. In ready state, a charge should be apparent at 13.9-14.1 VDC ( all readings approximate ) As Pat said cold weather and that puny bat do not get along well. I agree with his battery tender suggestion, if you have a garage environment situation. :rockon:

 

Patrick-
You're correct, about 3 miles each way. Each trip can take anywhere from 10-15 minutes. What exactly is a battery minder?

Andy-
I do have a garage environment, luckily. I'll start checking the battery level, that could be really helpful.

Tom-
Should I make sure the radio is turned off before shutting the car off so it isn't running when I start it?

Basically as soon as I start the vehicle it's in Ready mode, within about 2 seconds. Is that normal? Is that 2 seconds really important in drawing off that particular battery?

Thanks for the quick response and I'm sorry if I'm asking stupid questions.

~Amanda

 

Ques. to Tom. Probably a minor initial drain, but better to just keep radio off when not actually using it. Q. 2 Yes Ready is normal in about 2 sec. Excessive and unneccesssary current drains occur only from: not closing door, trunk etc. and happen in hours, not seconds. The design of the charging sys and the 12v battery is sufficient normally, as long as the owner doesn't start out with a weak battery.

 

Once the Prius is in Ready mode, the drain from the radio or any other normal 12V device does not affect charging of the 12V battery. The 12V bus is powered from the inverter. The problem with charging the 12V battery is that the Prius keeps the 12V bus at an optimum setting for running electronics, not an optimum setting for charging a battery. The result is a relatively slow rate of charge.

Those short 3 mile trips don't provide much time for recharging. If you don't need to drive farther on occasion, you may wish to add a battery minder to keep the 12V battery topped off.

Tom

 

Hi Amanda,

I'm talking about a low-current battery charging device that can be left on indefinitely. Some examples are listed below. These are not suitable for use if a battery is very discharged; in that case a more conventional battery charger is needed.

Batterytender.com - Home of All Your Charging Needs
Battery Chargers by BatteryMINDers.com

 

my 2003 went dead when it sat for a month. it'll last a week without driving it. The battery is expensive - the dealer quoted me $175. I'm thinking I'll buy a 12V motorcycle battery when I need to replace it.

 

Your on the right track. Almost any battery might be better than the OE. Wet cell, dry cell, AGM, whatever. Since the OE is something like 32AH, it's possible that a smaller battery would charge better.

 

I just checked using Andy's instructions and read 12.3 volts. Perhaps the difference is the on-state I picked? I pushed the power-on button without pushing on the brakes at the same time. I know there is a name for this state -- sorry for my ignorance.

Any advice whether it is time to change out this battery ?

 

Sounds like you picked ACC-ON, where the MFD is on but the instrument panel warning lights are off. 12.3V is OK but not wonderful. Your battery will probably last for a while, if you want to be safe you may want to replace it before next winter arrives.

 

Thank you Pat.
Was my test the equivalent of checking with a voltmeter on the battery itself ?

 

Mostly, except the voltage reported by the MFD secret screen may be off a few tenths of a volt compared to using a digital multimeter, and you can't measure IG-OFF battery voltage.

 

Am I right in thinking that a direct voltage check while the car is Ig-off would likely be a bit higher than what I did, since no electrical drains are occurring?

Jayman posted in another thread that he uses a trickle charger -- presumably related to living in the frozen tundra. My car lives in a snow climate, but nothing so extreme. Do you think the charger would extend this battery's life a couple of years ?

 

Yes, the IG-OFF voltage should be a bit higher than the ACC-ON voltage.

The trickle charger won't hurt and may help, if you don't drive your car frequently and long enough to keep the battery charged up.

 

Thanks again, Patrick.

Batteries are *such* interesting creatures. If I was 18 years old, I would be tempted to make them a life-long interest and endeavor.

 

I owned a 2005, driven daily, for two years, I did leave it sitting at home many times for up to a week with the Smart Key System on and never had the 12 V battery drain out and die on me.

Now I have a 2007, with 23000 miles, driven daily, and the 12 V battery is showing signs of a weak cell.

Background info. 5 days a week, round trip to work, 13 miles each way, 30 to 45 minutes, in the last month, I did not use headlights or heater or AC. 30% of the time I will use the freeway, 70% I will use streets for the round trip.

I started finding the clock not keeping the correct time 4 times when I started up on after sitting for one day.
Checked this forum and found out how to read voltage on the MDF.

Checked when it was in the READY mode. Reading was 13.8 Volts.
Checked when it was in ACC. mode just after driving and in the morning.
Just after driving 12.2 volts, load test with headlights volts drop to 10.8.
Morning test readings 12.0 volts, load test readings 9.9 volts.

After reading every post under this title, I think Toyota may have, had some bad batteries in supply line when they bulit my car or replaced other batterys. One group of batterys were border line when made and most went to the factory and some went into the supply system for the dealers.

If it was in wiring when the car was bulit, it would most likely be happening to large number of owners. I did not see any postings about problem after the 12 volt battery was replaced and at least one posting told of twice on the same car and it need two new batterys.

 

Somebody emailed me about this, so I thought I would offer some comments

First, never use a conventional trickle charger on a battery, as it will overcharge and ruin the battery. I use a battery tender, this model from VDC

BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) :: All :: Battery Chargers by BatteryMINDers.com

I had problems the first winter with my Prius. Even though at the time I had a condo with heated underground parking, my commute was under 15 minutes in temps down to -40

With constant use of electric rear defrost, headlights, max heat, and short commutes, the battery drained. Using the Battery Minder overnight solved that problem

The Prius taxis here don't have a problem as they are usually left in Ready 24x7

I sometimes have to be away for upwards of 3 weeks on business, and have also noticed the Battery Minders make a big difference in how long the batteries last. Nothing worse for a battery than being allowed to sit and slowly discharge

 

I have an 05 with 77,xxx that lost the 12 volt bat. at the end of a week of really bad heat wave here in St. Louis, but it was just a syphtom of my problem which actually was a result of the engine not running at idle when it should have. The mass air flow sensor wouldn't let it, so just 2000 over my extended warrenty I dropped about $425 on the sensor and $150 on the overstressed battery. I doubt that the battery would have recovered from the 10 volts it was reading at anyway since it was 4 1/2 years old. The extended warrenty was a waste of $1100 with no other issues covered.

 

I'm sorry to hear that. Was the MAF really kaput, or was it just dirty? Unless a definite code was thrown for the MAF, I would have tried cleaning it first

This is the MAF before cleaning



This is the MAF after cleaning. The bulb thing is the IAT sensor, which is part of the MAF



Inside the MAF barrel are the two hot wires, which are cleaned with the appropriate MAF cleaner. You can barely see them here



I'd also wonder if the TB needed cleaning, older Prius cars can have sticky TB blades, which cause problems

 

Don't believe it...If you drive your car once a week then you are fine.
If it keeps going dead. Are you sitting in the car with it powered off? Then the lights are staying on.
If you dont drive it for 5 days, and it goes dead and you have the remote keyswitch special dobber, turn it off under the steering wheel. Then just use the button to unlock the car.
The 12volt battery is very small in amps, and is only used to boot the computer and run the 12v stuff. unlike a regular car which needs a powerful battery to run the starter.

Dealers often say things they know nothing about...salesmen are the worst. Often they are uneducated and rude and crass. Ever here them talk trash about thier customers after work? Service writers are second worse. There job is to write money tickets, not solve your piddly little problem.