12 volt battery drain? or Converter Charging??

The fact remains that an AGM battery does ***NOT*** need higher charging voltages.

 

You claim that everything you've read supports your belief, yet the one quote you proffered says in essence that [6 cell] AGM batteries can be charged at 14.4 V or higher without problem. This implies that lesser voltage is not adequate for fully charging.

This supports everything I've read on this subject says that 14.4 - 14.8 V is what is required for bulk charging.

Without dwelling any further on this, it does seem you are contradicting yourself. Meh, maybe it's just me.

In any case I'm going to leave it there. We will just have to agree to disagree.

 

Completed the parasitic draw test today with my new meter. Prius is only pulling 150 - 200 m(A) when off. I also noticed the battery was showing 12.5V from 10.5 after a 5 minute drive down the road. I'll be purchasing a new 12V battery locally so I can actually use the warranty if needed. Thanks for your help. I'll post an update once the new battery is purchased and installed. Of course, I will make sure the new battery is charged before installing.

 

If your measurement is accurate, that reading is way too high. The quiescent current draw should be around 20 mA. The car must be IG-OFF, doors/hatch locked, and the Smart fob needs to be 15 feet or more away from the car.

Consider if the car is drawing 0.2A continuously: In 24 hours, that is 4.8 Ah. After a week, that is 34 Ah and the 12V battery will be dead.

 

That was a miscommunication on my part. The actual reading was .01 to .02A.

 

It does not say "or higher without a problem". How about you cut and paste a quote.
Even if it did say that, there is no implication that less is not adequate; that is an imagination, not an implication.

And what exactly do you mean when you use the term "bulk charging" ??

You still have not provided any reference that says an AGM REQUIRES a higher charging voltage.
That is THE question at hand.

 

Actually, it certainly does - word for word - and I have (see post #37). I can't help it if you can't be bothered reading what I post (or what you quote - for that matter) to support my claims.

And now, you are saying that even if your quote does say that (you didn't even bother to look and see if it did), you just want to brush it under the carpet as it does not support your position. I also did not say "less is not adequate", and neither did you. You said higher is not required, which is what I dispute. A lower voltage will add charge to an AGM, but I want you to show me a reference (or two) that supports your posit that it will fully charge the battery, which is what you claim.

Really??? And you are arguing battery charging with me?

As you are the one challenging everyone with your claim, it is really up to you to supply references to support your proposition.

I do not claim to be all knowledgable in this area and I am open to be wrong and I am certainly willing to learn, but in order for me to be convinced, I need more than "just because I say so" from some self-appointed "expert" on the Internet. The only reference you have supplied, does not support your proposition, as I have tried (in vain) to point out.

Without the introduction of some new authoritative factual information, there is no point in continuing this discussion. I don't care how many times you shout at me that "an AGM does NOT REQUIRE a higher charging voltage", that alone will not convince me. Please supply some supporting authoritative references to support your claim. You are the one that raised it, it is your responsibility to provide the references to support your claim.

And just to be totally clear, I'm not saying that you can carte blanche apply an unmetered 14.4 - 14.8 V charge to your AGM as the opening sentence in your Battery University quote quite clearly states that AGM batteries are sensitive to over charging. That is why I advocate the use of a smart charger that monitors voltage and current and adjusts as necessary depending on where it is in the charging cycle, and why daily charging is probably a bad idea if your a battery is not significantly discharged. However, if your AGM (or any Pb/A) battery is deep cycled, it should be fully charged as soon as possible.

 

I am going to quote charging information for AGM, and flooded lead acid batteries from possibly one of the top battery manufacturers in the world. "Rolls Surrette". This information can hardly be dismissed as "quote marketing hype". I cannot replicate there charts here as they are copyright, but I can quote the information that is available on there web site for all to see.

AGM batteries. (12 volt)
Charge at 14.82 volts at 20C (68F) for both bulk and absorption stages. When current falls to 2 amps float charge at 13.77 volts. At different temperatures voltage correction will be required.

Wet cell batteries. (12 volt)
Charge at 14.4 volts at 20C (68F) for both bulk and absorption stages. Float charge at 13.1 volts. Charging times are calculated depending on battery capacity. At different temperatures voltage correction will be required.

From this it can be seen that the AGM charging voltages are somewhat higher than than flooded batteries.
Trojan batteries another well respected manufacturer produce similar figures.

John (Britprius)

 

Just found this thread, have been struggling with the exact problem the original poster and now Daniel have described. Have gone through 3 optima batteries in the past year. I will post more details tomorrow, I have been up all night scrolling through the battery charging debate.

Also would like to track down the thread about the stuck relay.

 

You need to figure out whether the issue is a problem with your car or a problem with the 12V battery.

1. How many miles / year is the car driven? If it is driven 7,000 miles per year or less, get a good battery charger intended for AGM batteries and use it at least monthly, overnight.
2. Measure the quiescent current draw from the Prius using a digital multimeter, when the car is IG-OFF, doors/hatch are locked, and Smart fob is more than 15 feet away from the car. This requires unbolting the negative battery cable where it attaches to the body and putting the meter in series, placing it where you can see it with the hatch closed. Make sure you do not try to turn on the Prius when the meter is inline as most multimeters are rated to handle up to only 10A current. The reading should be ~20 mA or less after the electronics settle down. If much more then your car has a stuck relay allowing some electrical circuits to remain powered up.
3. Did you fully-charge the replacement 12V batteries prior to installation? Several posters reported the Optima batteries they purchased were in a semi-discharged state. That combined with low driving usage will result in a failed battery pretty quickly.

 

Patrick,

Thanks for the reply. I also have a 2007 Prius. Here are some answers:

1) We definitely put more than 7,000mi on the car per year, although I did go ahead and get a charger that will charge AGM batteries when I got this 3rd Optima Yellow Top.
2) I need to do this, can anyone recommend a good multimeter for the least amount that will suffice for this task?
3) We did not charge either of the 1st 2 batteries with a charger. I have purchased one now, to keep this battery alive until I can figure out what the problem is. I've charged it overnight until it reads full about 2 times a week.

The first battery lasted 5-6 months, the 2nd lasted a little over 1 month. With my limited knowledge of these things, I've suspected the answer lies in step 2. and finding where something is drawing too much power off the battery.

Thanks,

Jeff

 

2) You can spend ~$20 and get an OK digital meter:
Amazon.com: digital multimeter

I personally own several digital multimeters, including an older version of this Fluke model. Fluke makes very high quality meters:
Amazon.com: fluke 87

 

I'm also new, I'm having the same issue, jump starts don't work any more, slow charging lasted a few weeks. I saw something on here about the clamps having to be changed when OPTIMA BATTERIES are installed, can I see that link? I can't seem to rediscover it. My next step is try to find a fuse or bad circuit. I've found a lot of threads that start with the 12v battery problem and never end. If someone does solve it they don't seem to write back and explain it.

 

MOst of them end replacing the battery, making sure it is initially fully charged and watching it for a few days to be sure it stays charged.

I suspect that some are embarrassed to come back and report that the fix was simply changing out a weak battery.

 

Welcome to Prius chat. ^^^ Totally agree with Easy Rider.

Either you haven't found good threads, or you haven't persevered to the end, in either case almost all cases are resolved by replacing the 12V battery, which from what you've said, is almost certainly unserviceable. Most of the threads that go on and on, the OP does not seem to want to accept the battery is dead.

You will only need to do this if you buy the wrong battery -- one with standard posts (rather that JIS), or the posts on the wrong side.

No, the next step is to confirm what state your 12V battery is in and replace if necessary.

For the record, Optima batteries are not the best option, but it is your money.

I hope you can resolve your problem, and don't forget to post what you did to resolve your problem.

All the best.

 

@ horstnam

Here are some alternative battery choices.

Personally, I'd just install the Toyota OEM battery for SKS (S46B24R) as it has a good guarantee and has been proven to last well, provided it is looked after (as is true with any battery). If your Prius does not have SKS, get this one anyway as it has a higher aH rating (45 aH vs 36 aH), but you will need to change out the Toyota battery tray/clamp assy as mentioned in the post to which I linked.

All the best.

 

Following up on this more than a year after I solved my problem (not the original poster)

It turns out there was a parasitic draw that was slowly draining the battery with each use. There was a 30amp fuse in a 7.5amp slot in the main fuse box. Traced it back to Toyota service center simply putting the wrong fuse in when my wife had a separate issue repaired. We didn't end up needing the multimeters, just looked closely at the fuse map on the top of the box.

I simply replaced the 30 with the correct 7.5 and have never had an issue since. So the problem wasn't really with the battery(ies) at all. It was Toyota service center all along. I will definitely blame them since apparently they installed the wrong fuse in the first place, but also because after multiple trips to them to figure out what went wrong they never figured it out. They gave us at least 3 incorrect diagnoses before I threw my hands up and had to figure it out myself.

 

The installation of a larger fuse by itself will not cause a parasitic drain.

 

As Patrick correctly pointed out the rating of the fuse will have no effect on battery drain. The only down side of fitting a larger fuse is reduction in protection of damage to components or wiring (fire risk) due to excess current being allowed to flow under fault conditions.

John