12V Battery Voltage Management

OK, my 12V battery measurements with Prius turned off:
After my 10 mile/30 mins commute: 12.89V
After 30 mins rest: 12.95V (clueless why higher, temp change?)
After door opening and brake pump action: 12.82V
10 mins later: recovered to 12.95V

My take: the door opening is indeed negligible on battery SOC.
More testing to follow on weekend. there could be some impact from emissions pump action hrs after a shutdown.

I thought about it some more.

The truth is, there is no way to know for sure short of some documentation from the battery maker or OEM specification.

The fact that the battery fails so quickly after a few full discharges makes me agree, it is not a deep cycle, and just a regular SLI (starting) battery.

Deep cycle battery makes sense in prius only if people leave the car unused for longer periods or keep leaving lights or other loads on.

 

I was saying the same in different words. ONLY worth to spend on the deep cycle battery if the owner use pattern require it ... as you said ...

Managed to measure the Voltage of the battery this morning. Last night I drove about 2 hours then break for 2 hours and back 40 minutes. Not sure this was enough to fully charge the battery or not.

This morning it was 12.60-12.61V ... again I purchased this Prius in July 2009 and it was manufactured in May 2009 according to the label. So the battery is definitely over 3 years old.

I will take measurements on Monday morning since over the weekend I usually only go local so it will have little or no charge for 2 days ...

 

AGM deep cycle batteries are used in UPS ( uninterrupted power supplies ) these batteries are float charged at
12.8 to 13.2 volts continuously and have at typical life of 10 to 12 years with rarely being cycled at all. Most AGM battery manufacturers say to keep there batteries fully charged when not in use to prolong the life of the battery.

In my opinion there is no substitute for AMP/HR capacity, but totally agree that you cannot take out of a battery amps that you have not put in.

In the UK we have many well known manufacturers of AGM deep cycle batteries of around 60AMP/HR that are the same size as the Prius OEM, and is very similar to a battery available in the US. Check out Ebay item no 270777983177, this battery is 65AMP/HR. This battery should give months of standby use in the Prius.

 

But what is your point on this ... do you suggest to replace the battery ??? Guess not because UPS batteries as you say have almost never have power going out of the them. But prius DOES draw power (real question how much ) when just parked some estimate 15mAH my estimate was 100+mAh ... so this is perhaps NOT a good comparison ...

Again, I think (never tested) but UPS batteries designed to do something very different job .. and may (or may not) work in a Prius ...

Please give a little more either tested data or theoretical argument why they may or may not last longer ...

I have probably one of the oldest Prius 2010 I got it july 2009, and the battery shows NOW regularly 12.4 12.5 in the mornings and coming home standing in the garage during the day 12.2 - 12.3

So YES I am getting a little bit worried about this ... but like to hear from people with 2010 priuses if they HAD to replace their batteries ......

 

The UPS batteries are the same batteries as used in disability scooters and wheel chairs, they are capable of both standby use and deep discharge without damage. They also size for size have a greater amp/hr capacity than the much praised Optima (getting close to double the amp/hr capacity 55/65amp/hr) not that I am knocking Optima's product, and substantially more capacity than the OEM battery. Most of the reason for this is the spiral wound type of batteries poor use of space loosing about 23% of it's base area compared to flat plate construction.

This obviously means UPS type AGM deep cycle batteries can last longer when the vehicle is not in use, or if the dome light is left on for a couple of days. Also it's depth of discharge for any given amount of discharge in amp/hrs will be less in percentage terms against lower capacity batteries causing less long term damage and an improvement in life expectancy.

As batteries age they loose capacity, and the larger the original capacity of the battery the larger the amp/hr capacity is left. eg 50% loss of 30amp/hr leaves 15amp/hr
50% loss of 60amp/hr leaves 30amp/hr

The price in the UK of UPS type batteries is less than the OEM battery, with dependent on manufacturer up to 4years full replacement guarantee.

I have one in my Prius and have never seen a voltage after standing for 2 or three days of less than 12.7v measured with a calibrated Fluke DVM, and I do not use the car every day. I will reiterate that you cannot take current out of a battery you have not put in.

As an experiment I tried my Prius with a 7amp/hr alarm battery and had no problems at all but I would not expect this battery to withstand many days of non use of the car.

In short if you use your Prius every day for 30minutes or more and never leave the dome light on the OEM battery is fine. If however you do not use your car for long periods (parked at the airport or are regularly away) and unable to keep the battery on charge, or may leave the dome light on for a couple of days choose the largest amp/hr capacity battery you can find that will fit in the small area that is designed into the Prius.

 

I wouldn't worry about it. My car is only about 9 months newer than yours, and I measured the voltage at 12.50 V when I'd had it for a month and a half. Also, that measurement was taken with all doors closed and everything off - if you open the hatch to take the measurement, the cabin lights will turn on, along with a few other things; in that condition, I measured 12.32 V.

I did drain the battery completely (0.4 V) about a month after I took those measurements, but it's been fine ever since.

That said, if you expect to be in a situation where a dead battery will cause you significant trouble (i.e. your boss has told you you'd better never be late to work again, or you regularly stop in very remote areas), you may find it worthwhile to replace the battery long before it's needed, or at least carry some backup that will allow you to start the car if the battery dies. I considered putting a 12V UPS battery in the car along with some wires to hook it up - in the event of a dead battery, I'd disconnect it (to avoid a load on the good battery), pull the ABS fuses (to avoid the brake pressurization putting a large load on the good battery), hook up the UPS battery, start the car, replace the ABS fuses and dead battery, and hopefully not break anything in the process. That's the theory, anyway. But I decided that since I was most likely to have a dead battery while at home (where the car often sits for a week without being used), I'd rely on that to have access to anything I need.

 

I drive the car every workday except when I am on leave but even then I would drive .. .very rarely I am away (bad times ...). So the battery is charged regularly .. still seems that is loosing its capacity which is expected I guess....

What I am trying to figure when I would really need to replace it .. and with what .... normally i would expect 5 year out of a car battery (even a little more ) I have not kept my first prius long enough to find out ... but this one I am planning to keep... so I am asking other prius owners who had the car longer what is the experience.

I do not have any problem really, just see the voltages lower and lower over last 6 months since I am looking. I do not know what it was new because I did not check. ....

 

I'm building an electric go kart type car, and I need a decent amount of power. I'm using Thundersky 40Ah 3.7V batteries x 38 to get 120V system.
Click here to procure more information kollagen intensiv

 

My Prius battery is three years old with 51,000 miles and a consistent overnight voltage reading of 12.79 to 12.8 after cleaning the battery terminals. Before I cleaned the terminals the reading was around 12.6. I suggested battery terminal cleaning on another thread and it was not universally appreciated; but it is easy, inexpensive and you may find it improves your voltage readings. I fully expect my Prius battery will last 5 to 7 years.

Servicing the battery generally involves:
· remove the battery cables and hold-down bracket(s),
· clean the top of the battery case, terminals and cable ends with a battery cleaner,
· using a battery brush with soft brass bristles, lightly brush the battery terminals and contact areas inside the cable ends until they are bright and shiny,
· reinstall the battery cables and hold-down bracket(s),
· coat the reinstalled battery terminals and cable ends with a battery terminal protector.

BTW if you want to check the voltage without the brakes cycling on, enter from the passenger (not driver) door and reach over the console to pull the hood release lever. Opening the passenger door does not cause the brakes to cycle.

 

Yes but doing this will reset quite a number off things unless I find an alternate power source to keep the 12V perhaps a battery tender connected under the hood before disconnecting ... My question is that safe ?

The last part is very good tip I did not know.. I do not need the hood opened I have a SGe installed on the dash which will show voltage pretty accurately (as it turned out I was wrong on another thread the OBDII bus ALWAYS powered).

 

More often than not any voltage drop on the Prius battery cable connections is on the negative lead where it fastens to the bodywork because of corrosion between the terminal end and the steel body. This can be disconnected without loosing settings by fitting a jumper wire to the negative battery terminal and any clean bolt in the trunk area, then disconnect the negative lead for cleaning at the body.

 

Connecting a power source under the hood will result in the positive cable being "live" after it is disconnected which in my opinion is not safe because if you are not careful and it touches a ground it could cause a spark which could injure you and/or the vehicle.

I just disconnect the battery and deal with the few minor affected items, which are:

• radio presets (will have to be reset)
• auto window up/down (just need to completely lower and raise the driver window once holding the control lever each way)
• trip mileage and mpg readings (current values will be reset to zero and begin again from that point automatically)
• EV/ECO/PWR/mode will go to the unlighted BASIC mode (just push the button for desired mode)
• the powertrain module(s) will be reset and will relearn themselves after a few drive cycles.

I have a couple of the battery minders which plug into a cigarette lighter/power plug sockette, but they don't work all that well either. I have found it actually takes me less time and effort to just disconnect the battery and do the resets afterward, than hooking up devices beforehand and trying to prevent losing the presets.

Voltage loss can occur in any connection on the positive or negative side of the system due to high resistance in the connection, usually caused by corrossion or oxidation. Why do you think the negative cable to body ground is most susceptible? Have you seen this?

 

Yes the negative lead to body connection is more prone to problems as it is brass connecting to steel with a steel spring washer, the steel parts prone to rust. It has been reported on a number of occasions as a fault area on PC, both for corrosion and not being tight.

Lead to brass the other end of the cable is not so prone to corrosion mainly because the battery used in the Prius is sealed and under normal circumstances does not vent but if it does the sulphuric acid fumes are vented to outside the vehicle via the vent hose, and not onto the battery terminals as with cars with the battery under the hood.

 

Yesterday, when testing my OBDScan I found 11,5V on the port.
Went for a "tour" of 15-20minutes trip, and checked again with the onboard-meter, 12,0V.

I'm now definitely worried about the 12V battery...
My Prius will be 3 year old in 2 month time.

 

Remember when you open the driver's door the battery takes a HUGE hit ... open the other door and turn on the car that way ... so the break pre-charge doesn't happen and you may have a sitting voltage (like after the car sitting a few hours 6-8 hours ).... if that is 11.5V that is almost dead
Yes those numbers are low ... what was the temp ????

15-20 minutes is NOT enough time to charge the 12V battery from a low SOC ...

 

Thank you szgabor.

The temperature was really mild (inside building garage, 16ºC/60ºF).
I will measure with a multimeter today just in case.

 

That is OK temp to measure (very cold weather will show lower voltage and that could be misleading)

If you have a multimeter you can even directly measure at the battery .... messy if you have stuff in the trunk...
But as I said before, you can enter from passenger side ... pop the hood and then measure there. I used to do that when my last prius was getting about 3 years old.. (I learned this trick here so I am sharing ...)

Also 3 year or even mileage matters but, the overall "life" of the battery matters more if you had the 12V drained several times ... and both cold and hot operation matters a lot it will be in a worth state.

Again 15-20 minutes is NOT enough to charge if it was very low ... if you can safely do so leave the car in Ready ON mode ... 30-40 minutes or more ...ICE will come up but not that much (not good if the weather is pretty cold like now here)

Another way to tell, since you have some scanner ... the car will keep charging around 14.5-14.6 while in parked but if you put it in drive (turn off everything like lights, A/C, fans etc... ) the voltage on the scanner should quite quickly drop to 12.8 - 13.1 level .... BUT again any load will raise it back ...this how you know that the car computer thinks it is charged... then after let say couple of hours do the above to check with multimeter or scanner

Good luck !!!

 

I am a low mileage Prius owner and had problems with the 12V battery when the car was about a year old. The battery was replaced under guarantee. I know others who have had similar problems. My Toyota dealer said that the problems resulted from the 12V battery not receiving adequate charging because of limited use of the vehicle and recommended a regular top up with a battery charger. He specifically recommended the tecMATE Optimate4 charger and that is what I now use. The maximum charging current is listed as 0.8Amps.
I have had no battery problems since getting the charger.

 

Sound perfect advise AND makes sense !!! If you do not drive it regularly or putting it in Ready ON. About 2 maybe 3 weeks 12V is discharged !!! and same would happen if your daily commute just too short ...

Good Luck.... and yes if you have a garage using a battery tender stuff just makes sense...