12 volt battery drain? or Converter Charging??

The Optima battery at 12.6 volts is no where near fully charged. It should read at leased 13 volts.
At what rate of charge in amps did you charge it? A 6 hour charge would need a minimum of 7 amps for a discharged battery, and as stated before if the charger is only for ordinary car batteries "no AGM setting" it will not fully charge an AGM battery that the optima is.

John ((Britprius)

 

Battery is reading 12.65 volts this morning. Looks like something is draining the battery. My very old multimeter recently bit the dust, I borrowed a basic multimeter to read the voltage, but it won't measure amp draw. Looks like I'll need to pick a new one up today to complete the parasitic draw test with the hatch closed. Any other suggestions?

Thanks!

Just read the post above. I'm using a CTEK MUS 4.3 charger and using the recommended snowflake.

 

How do you figure that something is draining the battery, if it measured 12.63V last night and measures 12.65V this morning?

It wouldn't hurt to measure the vehicle quiescent current draw for future reference, it should be ~0.02A (20 milliamps or so) but it is not obvious to me that this is an issue.

If you are using a charger which is supposed to be compatible with AGM batteries, see what the voltage is at the time that the charger thinks the battery is charged. Maybe the charger is cutting off power before it should.

 

Hi Patrick,

Last night I disconnected the 12 volt battery from the Prius after charging it (fully according to the CTEK charger I was using). The result this morning was a battery at the same voltage as the night before. Every other night for the past month, I've come out to a dead battery the next morning (without disconnecting the battery). I did an initial draw test a couple of weeks ago and discovered the dome fuse was pulling half an amp, but I wasn't leaving it hooked up more than a few seconds and I had the hatch open. I'm going to do another test today as soon as I pick up a new multimeter.

 

That is mostly outdated information.
All but the cheapest chargers these days will do AGM batteries just fine.
If your charger is more than 5 years old, maybe not but even some of them are OK too.

 

When I posted this information we had no idea how old or what charger the OP was using, further there are still many cheap basic transformer type of battery chargers on the market making the information still very relevant. The very fact that the battery after being "fully charged" (quote) was only at 12.6 volts suggests that a charger with insufficient output voltage was being used.
The old style battery chargers are reliable and many people will have chargers that are 25+ years old and continue to use them without problems on normal lead acid batteries, but do not realize that although they may put a charge into an AGM battery they are not capable of fully charging them.

John (Britprius)

 

And I am flat out telling you that is bad information......or at least grossly incomplete.

The 12.6 reading is much more likely to indicate a slight loss of capacity in the battery itself BECAUSE......ALL BUT THE SMALLEST AND CHEAPEST 25 year old chargers have more than enough charging voltage to fully charge any AGM battery. Some don't but many DO.

You are incorrect to flatly state that NO old charger will fully charge an AGM battery.

Many of them WILL, partly because the charging voltage was not decreased as the charge increased as much with a dumb charger as a recent "smart" charger would.
That is why an "old" dumb charger would "boil" fluid out of a wet cell battery if left connected too long.

And finally, even a float voltage of 13.8 will eventually bring a healthy AGM up to a full charge.
It might take several days but it will happen.......if the battery is healthy.

 

I hooked the meter up to my battery while it was charging last night and it read 14.7 volts. For what it's worth, my two year old charger is supposed to charge Optima batteries using the "snowflake" mode. I'm hoping to do a parasitic draw test this evening and really appreciate the information provided so far.

 

Now I will correct you. An AGM battery to be fully charged needs a voltage "depending on temperature" of around 14.8 volts. 13.8 volts will not bring the battery up to full charge, and is why 3 stage chargers are used dropping to 13.8 volts to keep the battery float charged. I will con seed not all old style chargers have insufficient voltage my wording being a little loose, but they were generally set at a voltage output of 14.2 volts.
Further if this battery "an Optima yellow top" has lost sufficient capacity in 18 months of use to drop it's voltage to 12.6 after being fully charge then it is not going to last very long. The battery "going from the numbers presented by the OP" was taken from 10.5 volts "100% discharged" to fully charged in 6 hours at a maximum charge rate for the charger of 4.3 amps " maximum possible input 25.8 amp hours. This into a 38 amp hour battery. Does not add up.

John (Britprius)

 

A quick search yielded this:
As with all gelled and sealed units, AGM batteries are sensitive to overcharging. These batteries can be charged to 2.40V/cell (and higher) without problem; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive. See Charging Lead Acid.
Obtained from:
Absorbent Glass Mat (AGM) Battery Information - Battery University

Which seems to indicate, as I was trying to say, that an AGM battery does ***NOT*** need a higher charging voltage.

If you have authoritative documentation suggesting otherwise, please provide it.
Otherwise, I'm done.
P.S. Marketing hype from a company trying to sell you a new battery charger does NOT qualify as authoritative.

 

I think your quote supports what Britprius is trying to tell you, and does not at all support your position that "an AGM battery does ***NOT*** need a higher charging voltage".

What are your qualifications to make the statements you're making, if I may ask?

 

From Optima's own instructions:-
Battery Charger:
Cyclic Applications:
14.7 volts, no current limit as long as battery temperature remains below 125 F (51.7 C)
When current falls below 1 amp, finish with a 2 amp constant current for 1 hour.

My addition to this is:- that to raise the current to 2 amps for the final hour would mean raising the voltage above 14.7 volts to achieve this charging current, typically around 15 volts. A voltage of 13.8 will not charge the battery fully.

Finally why do the better chargers come with an AGM setting if it is not needed.

I will not go into my qualifications, but I did attend several universities backed up with 50 years in the electronics industry.

John (Britprius)

Cyclic Application Cyclic Applicatio

 

Do we have a reading comprehension problem here ??
It says nothing of the sort.
It says that the charging voltage required for an AGM battery is LESS, not more, than it is for a flooded cell type.

My qualifications:
I can read and understand English......most of the time
AND
I've been an Electronics Engineering Technician for about 50 years, part of that with AT&T and Bell Labs.

 

That is an ASSumption on your part that is not supported by all of the information that is available.

I have in my possession a total of 4 small battery chargers, all less than 10 years old, and none of them has a separate setting for AGM.
But all 4 bring an AGM up to a full charge quite nicely.
I don't think I've seen one that DOES have an AGM setting for years.

The reason likely is that they can put in a switch and a couple of resistors (for instance) that cost them about 20 cents and charge you $20 dollars more for the extra "feature". YOU, not me.

Most people don't have access to a charger that works in a constant current mode; the electronics to accomplish that is fairly complicated and improper use could be rather dangerous.

And finally, the company that makes the Optima is known for marketing hype that they try to pass off as science.
Putting all of your faith in information from a marketing company is usually not a good thing to do.

I quit. You aren't listening.

 

We are not talking about charging on a car with an alternator. The Prius does not have one that charges the 12 volt battery directly "words chosen carefully there". We are talking about fully charging AGM batteries with a battery charger and more specifically an Optima although it makes little or no difference. I am myself using 2 Ritar AGM batteries "one in the Prius, and one in a caravan" and the charging instructions that came with them virtually mirror those of Optima except the voltages are a point or so higher for the Ritar.
Ritar produce there own chargers for there AGM batteries the output of all of the 12 volt versions is 14.8 volts.

John (Britprius)

 

That counts as anecdotal evidence and by itself is virtually worthless.

A higher initial charging voltage would charge the battery faster, which the AGM can handle just fine since it has a lower internal resistance.
We weren't talking about that but about the "finishing" voltage and whether higher charging voltages are "necessary".

I once again ask you to provide a reference to information that indicates, like you claim, that AGM batteries REQUIRE higher charging voltages.
Everything I can find says exactly the opposite.

 

Funnily enough, I was going to open my reply with a similar sentiment. I though better of it as I try to argue with reason and logic, rather than personal attack. I also though I might come across as an @$$hole, so refrained.

Where?

From what I read in your quote from "Battery University"

the salient points are:

• [6 cell] AGM batteries can be charged at 14.4 V or higher without problem - this implies that lesser voltage is not enough;
• float charge should be reduced to 13.5 to 13.8 V - which the Prius does do;
• Automotive charging systems have a fixed float voltage setting of 14.4 V - Which the Prius does not;
• [Float] charging a sealed unit (such as an AGM) could expose the battery to undue overcharging on a long drive due to the fixed float at 14.4 V;

None of that supports what you're saying.

I guess this is one of those times your reading and understanding has failed you.

Well I, for one, am surprised. I would have expected that if you are indeed so qualified you would have a better grasp of your subject. Or at least, seeing as you come to this forum, you'd at least attempt to elucidate by reasoned debate and sound argument. From what I've read of your posts over many and varied subjects, across the forums, you'd just rather belittle, criticise, contradict and otherwise are argumentative to try and prove you are somehow superior to everyone else here. I don't claim to know everything and this is one of the reasons I come here - to learn. I find I learn very little from your posts. Mostly, I just get annoyed.

There is a very good book that I suggest you read "How to win friends and influence people" by Dale Carnegie, unless of course you have no interest.

And with that, I'll finish with one of your famous endings, "I'm done, you're not listening"

 

How about share this information with the rest of us ignoramuses so we may be lifted out of our knowledge vacuum.

I guess I'll get the usual response to such a challenge and get flipped the bird and told how we're not worthy to waste your time on.

I'm done.

 

I certainly am listening. I'm just not hearing anything that makes any sense.

The article mentions a float voltage for AGM at 2.25 to 2.3 per cell, which comes out to 13.5 to 13.8 volts AND indicates that it would be, or could be, OVERCHARGED at 14.4.

You have to think about it just a tiny bit but seems pretty clear to me.

And I offer you the same opportunity as him to come up with some reference that indicates AGM batteries ***NEED*** higher charging voltages than conventional wet cell ones do. That is all that I objected to initially.

 

Nice to know, it's just you don't come across as the listening type.

You are confusing charging (at 14.4 V) and float charging (at 13.5 - 13.8 V). The sentence that mentions the float charging is in relation to a car charging system that has a fixed charge rate of 14.4 V (which the Prius' does not) and how that will damage a sealed unit if allowed to happen.

You have to think about it just a tiny bit but seems pretty clear to me.

Your quote from Battery University is all the reference you need. You just have to think about it just a tiny bit more.