2007 12v battery dies (4th time)--please help

The Prius should be READY for at least 30 minutes every two weeks, to keep the 12V auxiliary battery and the traction battery charged. It appears that your parents' car is not driven sufficiently to keep the battery charged.

It is possible that the vehicle has a defect. To ascertain that, you would have to hook up a digital multimeter to the battery so that you can determine current being drawn when the car is IG-OFF and locked up. The current should probably be ~30 mA or so.


Assuming that the vehicle has no defect, then the possible solutions include:

1. driving the car more often
2. disconnecting the 12V battery when the car is not in use
3. or hooking up a battery tender to charge the battery at a low rate when the car is not in use.

After the 12V battery is jump started, leave the car READY for an hour or so, so that it can charge up. Make sure that the battery polarity is correct as severe damage can be caused for a botched jump start.

 

This is most likely the result of the vehicle not being driven enough. The Prius with its unusual battery configuration and related systems is prone to this sort of problem. Being driven only 10 miles once a week is not sufficient to charge the 12 V each time. After enough cycles of losing charge it is eventually going to come up short. (My V8 Tundra would have a problem with this as well when I was in Georgia. I learned the hard way in cold weather when it was driven only a few times a week for a few minutes at a time. After about a month of this the battery was dead.)

It is of course possible that there is an electrical gremlin or that they are doing something wrong, but what you describe sounds more like a problem of not being driven enough to charge the battery.

One thing I did when I drew the Tundra battery down too far was to put a plug-in digital volt meter in the accessory slot so I could turn the key to check charge before starting, and I could see if it had enough charge retained when I shut down. This confirmed that the truck wasn't the problem, it was that I wasn't giving it time to charge--operator error. If the difference between volts lost each time and the amount recharged during the drive was 0.1 V it wouldn't be long before the battery was weak. (I found this little gadget by Whistler in a box of garage sale parts.)

 

Hi Bill,

Look at the instrument panel and see the READY light that appears after you have started the car and it is ready to be driven. Note that the READY light goes off when the car is ACC-ON (i.e., the MFD is on but no instrument panel warning lights are on) or when the car is IG-ON (the MFD is on and the instrument panel warning lights are on.)

You can cycle between IG-OFF (where the car is turned off), ACC-ON, and IG-ON by repeatedly pressing the POWER button while leaving the brake pedal alone. Then, when you want the car to be READY, just depress the brake pedal and then press the POWER button.

The battery tender has to be connected either directly to the 12V battery located in the passenger side of the hatch; or else to the dedicated jump start terminal within the main relay/fuse box located in the engine compartment near the inverter. This could not be connected through the auxiliary power port unless you have that port rewired so that it is "hot" at all times. Such rewiring would void the Prius warranty to the extent that the modification was shown to cause a problem.

It is highly unlikely that a Toyota dealer would agree to install an aftermarket modification, so you would have to find a local stereo shop to do that work.

Further, the Prius may not be the right vehicle for your parents if they have no reason to drive more than ten miles a week. (In that case, they may do well just to take a cab, saving all of the expense associated with owning a new vehicle.) Although a battery tender will take care of the 12V auxiliary battery, this does not help the traction battery which has its own charging requirements to stay healthy.

 

My first 8 months or so useage on my 2007 was about like what you described. I would turn the smart key off, had no 12 v problems. I was gone for a month, no problems. Since the cars are made to a good standard, it would be a suggestion to make sure they are not leaving something somewhere on and that they are turning the car off correctly? When I test drove before buying, several had dead batteries on the lot, due to salesperson errors.

 

Hi Bill,

Regarding 5), pls make sure that anyone who may be in a position to do the jump start recognizes that battery polarity is very important. A mistake can be very costly: at minimum, replacing the fusible link and a few other fuses within the main relay/fuse box; and at maximum, replacing the inverter for several thousand $s, due to a blown DC to DC converter within.

Here are two more items for your list:

6) Make the Prius READY for a 30 minute period, at least every other week. (Not necessary to actually drive the car during this time.) If 6) is done conscientiously, this should keep both the 12V and traction batteries in good shape, and reduce the need for 5).

7) Since the car will be driven < 1,000 miles per year, the engine oil and oil filter should be changed annually.

 

Patrick, <1000MPY, thats only 2-3 tanks/year. Any cosiderations regarding sitting long periods with E10 in the tank, water absorbtion? I assume that the bladder reduces the problem, but would you suggest any additives such as MDR E-Zorb to play safe?

 

Since the Prius is locked the hatch light shouldn't be the problem as the hatch is closed. If it isn't closed there will be 1 beep when trying to lock.

My mother has a 1999 Delta 88 and doesn't drive much, but more than your parents. The battery doesn't hold a charge but is not defective. The warning sign of "not got to start in the near future" is when 1 of the idiot lights comes on (security?). A jump & the car is fine.

IMO they just need to drive the car. If you swapped cars I'll bet your Prius develops a "battery problem" while the problem with their Prius is fixed.

 

Hi Dave,

Since Bill revised the estimate of his parents driving to > 5K miles per year, they are probably buying gas 1 - 2x per month - hence the gas should not be aging unduly.

I don't know how fuel additives would react to the resin bladder, so I am not in a position to say their use is good or bad.

 

Thanks Patrick! The reason it was fresh on my mind is that our Ford Club Wagon has two tanks, 18 & 22 gallons. It will go when the Prius arrives, but until then, I'm thinking of running one dry and throwing a bottle of MDR E-Zorb in the other, now that they're pumping E10 in GA.

 

Bill,

One other possibility came to me when looking at Jelloslug's "project car" thread. He shows a pic of a dealer installed alarm system that could drain some 12V. This is a long shot but is there anything like that installed on their vehicle?

 

I'd say that it's more efficient to plug a Battery Tender in after every drive, then have to do 30 minutes in READY (which would include a full ICE warm-up cycle). The BT that I have has leads that you can permanently attach to the battery terminals, leading to a set of SAE 12V connectors. Use that, and there's no way to screw up the terminal colors. Use zip-ties to route it, and you might not even have to open the hood to hook them up.

 

This is quite true with respect to the 12V auxiliary battery. However the battery tender does nothing for the traction battery.

Bill originally described a situation where his parents' Prius is only being driven < 1,000 miles a year. In that case the traction battery may not receive sufficient activity to keep the state-of-charge where it should be.

The concept of making the Prius READY for 30 minutes comes from TSB PG007-03 that provides advice about vehicle storage. Note that the TSB also suggests disconnecting the 12V battery if the car is stored for more than 10 days at a time.

Since Bill's parents want to be able to drive their car without reconnecting the battery, I suggested making the car READY for 30 min. every other week. This is overkill regarding the traction battery, but will ensure that the 12V battery stays in good shape.

Now that we have learned that the car is being driven > 5,000 miles per year, then if Bill's parents are willing to connect/disconnect a battery tender whenever they want to drive the vehicle, that should be sufficient to keep the Prius ready whenever they need it.

 

I've covered this in earlier threads, but I have been using the VDC Battery Minder for almost 4 years now, on my Prius, my FJ, and at the hobby farm my work truck and tractor.

It is absolutely safe to leave the battery minder plugged in 24/7, it won't cook a 12 vdc battery. The desulfation mode also extends the life and performance of conventional 12 vdc batteries

The battery minder won't help the NiMH traction battery. As Patrick stated, the car must be in Ready for 30 mins to properly charge the NiMH battery

 

You didn't mention what package they have. Do they have the Premium JBL sound system which if memory serves has a possible defect in the audio power amp that keeps the amp on all the time.

 

Hi Bill,

Regarding b) and c) of your list above, a digital multimeter would be sufficient to shed light on both items. To determine b), one would measure current drawn from the battery when the car is IG-OFF, all lights are off, and the car is locked. If much more than 30 mA, then some item remains powered on (Ed mentioned the JBL amp as one possible problem area, this was true with some early production 2G.)

To determine c), one would make the Prius READY, then measure the voltage across the 12V battery. The correct voltage is ~13.8V. If this reading is found, then the DC to DC converter is working properly, hence the battery will be charged by the circuitry (given due time). This is not like the alternator/voltage regulator setup on regular vehicles where the alternator voltage can fluctuate depending upon engine speed and the battery's need to be charged.

Regarding a) of your list, I've noticed some posters who have asserted that their dealer gave a passing grade to the 12V battery after a load test, only to find shortly thereafter that the battery has failed - hence I personally would not pay for such a test to be performed. My technique would be simply to measure the voltage across the 12V battery one hour or more after the car has been IG-OFF. If the voltage is much below 12.6V, it needs to be charged or replaced. If after charging and then leaving the battery alone for an hour, the open-circuit voltage remains much below 12.6V, then I would suggest replacing it.

The battery minder is a device that you can easily install and remove; there should be no warranty issue as long as correct polarity is observed. Actually, battery minders will usually have circuitry so that the device will refuse to function if it is incorrectly hooked up to the battery. Do a web search, or else visit your local discount auto parts store.

I recall your saying that your parents are in or near their 90s. My dad is 92 (and still driving his 2007 Prius 5K miles per year) so I can relate. It is a miracle every day that they can drive and not have an accident. Hence, the need to keep things as simple as possible. Good luck with the battery minder.