2005 Prius 12V Battery Questions

I got home and hooked up my smart charger.

1st thing: I was mistaken - my smart charger has settings for 2a, 8a, and 10a. There is no 5 amp setting.

2nd thing: I got home and the battery was resting at 12.7v. Im going to recheck it in a few hours and as long as its not resting at less than 12.6v, Im not going to bother charging it.

Patrick - if I need to, can I smart charge it at 8amps instead of 5amps that I indicated earlier? or should I choose 2amps?

 

Does your charger have a gauge that shows the actual current flowing to the battery? If yes, you can try using the 8A setting, but watch the gauge to see if it drops down to 4-5A pretty quickly. If it stays at 8A for an extended period of time, it would be safer to use the 2A setting.

 

Ok cool. I set it to 2amps just to be safe because it does not show the amps going to the battery. I have a variation of this charger, mine is very similar: Schumacher Speed Charge 12-Amp Battery Charger - Walmart.com

One last question: It gives me a selection of "regular", "deep cycle" or "AGM/Gel". I selected "deep cycle". Was I correct in doing so?

 

I'd select 2A and AGM/Gel. The lower charge rate is slower but you're also less likely to lose electrolyte.

BTW. Your new battery looks the same type as my original OEM one that lasted 8 years!

 

Will it hurt the battery if I leave it on deep cell 2amp? Its -7f outside right now and Im in bed. lol. If I 'have' to, Ill get up and go change it. But would it really lose any electrolyte at these temps?

I hope I have the same luck as you! 8 years is GREAT!

 

I would put in on the agm/gel setting. The other parameter may not fully charge the battery.

When that battery is fully charged, it should measure at least 12.8 volts at the terminal with no load.

12.7 volts is almost a 100% charge for a AGM battery.

 

No it shouldn't hurt. I think the charging voltage is just a little bit higher with the AGM/Gel setting.

Sounds like the best place to be in those conditions.

 

Ok so I had to go outside anyways, garbage cans blew over. I changed it to the AGM/Gel setting but it had already completed its charging process and was floating it at 12.8v, according to the display. Either way, I changed it just in case it went through another cycle, and left it connected for the night

I think I need a C-Tek charger....

 

Get a BatteryMinder 12248 like what I have. It is perfect for the Prius battery. Cost's a little more, but it is worth it in my opinion.

Doesn't surprise me that the charger already shut off. It should not take long since it was almost 100% charged at 12.7 volts.

 

Well.... I forgot to mention that I went out and checked it after it sat for a few hours and it measured 12.4v with a DVM across the battery posts.

I will check out that 12248...

 

Hmmm. 12.4 versus 12.7 is a considerable amount, but with the cold temps there could be understandable too. I don't have one of the fancy graphs that shows voltage drop with temperature change, but it does affect it.

If you haven't changed the charger over to AGM yet, do so and restart it and let it run all night. Then put the battery in and go with it. You can always top it off later on with the jump post if you so desire.

The one I have is 14 months old now. It will still hold a charge of 12.8 overnight after a full charge with SKS on. But after three days of sitting idle, it starts to drop off. This cold winter has really given the new battery a work out. But I am very pleased so far with what I have down here. And it has been very cold this winter especially for Houston. Several freezes and snow to boot.

Winter is almost over, so hang in there. The best is yet to come.

For reference purposes, the MFD on our Prius reads .2 volts less than the readings with a DVM.

When the 12 volt is fully charged and the ambient is 70F~ I get the following.

Accessory Mode: 12.6 Volts
Ignition Mode: 12.4 Volts
Ready Mode: 14.0 Volts

In reference to the above numbers and testing parameters. I only test the battery after it has been charged and allowed to set overnight to remove any surface charge. Also when running the test with the MFD, the only loads applied are what comes from cycling the power switch. I keep the headlights, radio, climate control, defroster, etc. OFF so I don't get excessive loads or voltage drops that could give misleading testing information.

I have a feeling your numbers will be similar once you put the new battery in.

Have fun, I think you made a wise decision!

 

BatteryMinder 12248 - Personally recommended to charge AGM 12 volt battery in the Toyota Prius

BatteryMINDer Battery Charger / Maintainer with Desulfator — 12 Volt 2/4/8 Amp, Model# 12248 | Battery Maintainers| Northern Tool + Equipment

Batteryminders Specials | BatteryMinders.com

 

That's probably just the surface charge dissipating. This is the reason it's usually recommended to do the voltage tests in the morning after the car has sat overnight, so it's truly in its "resting" state.. Otherwise surface charge can give noticeably higher readings.

Remember with battery voltage measurements there are a lot of factors that influence the results.
1. The state of charge of the battery.
2. The state of "rest" of the battery, corresponding the the presence of surface charge if the battery has been charged recently. (BTW, the opposite effect can also occur. A temporary voltage depression caused by surface discharge due to a recently applied heavy load current.)
3. The underlying health of the battery (as in internal resistance, electrolyte heath and sulfating etc)
4. The amp load on the battery.
5. The temperature.

Personally I think that point 4 is a major reason for some of the variability in reported voltage measurement made with the battery in the Prius. Even if you have the Prius fully off (and don't even bring the sks fob anywhere near it), many of the prius ECUs boot up when you just open a door or hatch. If for example you open the drivers door to pop the hood, instantly the 12V battery is under load current (yes even if you then close the door).

I experienced this first hand last week when I was measuring my 12V voltage, at the jumper point under the hood, car completely off and no key in sight. The voltage was 12.3 to 12.4 volts, and it stayed stable like that for about 15 minutes, then suddenly I heard a little relay click off and the voltage rose almost immediately to 12.7 to 12.8 volts. Clearly it had been drawing a reasonably significant current despite being complete off, and clearly something had eventually timed out allowing the Prius to go back to sleep causing the voltage to rise. I suspect that most people are measuring somewhat depressed voltages due to this load current whenever voltage measurements are made with the battery in car.

 

I too have seen what uart mentioned above about voltage levels changing radically even when the Prius is "OFF". One can simply walk by the car with the fob in the pocket and ECU's will fire up causing a load on the 12 volt. And if you open the door, the brake pump gismo (name I forget) fires off which pulls more juice too. All kinds of electronics in this car which can cause erratic behavior when it comes down to measuring voltage.

Those who are familiar with the Prius have probably seen this, but for newcomers it can tend to stretch the mind so to speak.

 

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Yes, but at least I did pay a lot less. Will it be worth it? I'll tell you in a few years, I can only hope. Hope to not find out sooner! The writeup I saw said the 38 amp-hr is 18% over the OE -- I don't know if that is so. Someone here will probably tell me. When I bought the Optima I had not heard about it requiring a bigger tray, or the troubles that people were talking about having with them. But, so far so good with mine. It is definitely hotter than my old one. I checked at the local dealer a while back and they wanted over $220 w/tax for the "bigger version" Prius OE battery.

Taking a philosophical view of things, if I had not run across the deal that I did on the Optima, I might not have replaced it when I did. I would not have discovered when I did that my old battery was down to 10.5v, and that might have left me, well, who knows where?

 

Yeah your optima sounds like it's fine 90miler. I don't see any reason why it wouldn't last many years.

 

Interesting about the Prius "sleep" and the battery voltage if you are standing near with the SKS - which I did have the FOB in my pocket when I was checking the battery when it read 12.4v.

Thanks for all of the help and advice!

 

Nothing you have said so far indicates that there is anything wrong with what you have now.

Note: AGM batteries are sealed and you have to hit one with a REALLY high charging rate to cause any loss of electrolyte......like 20 amps for a long time.

 

PriusGuy's battery from Japan has a different "date code" sticker than mine (mine had a J13, his has a 1/14), so it looks like they did away with the alpha code, which I guess is no big issue.

But, the counterperson told him Interstate made and delivered the batteries, etc. And obviously PriusGuy's battery is not an Interstate (I'd be more comfortable with the GSYUASA anyway).

So, I am supposing Interstate makes some Toyota batteries, but they are still getting the Hybrid 12V from Japan. As Patrick once said, that's a long way and a lot of cost to still sell them for $200USD. Not that I am complaining....

 

Heres what I think the Parts guy at the Toyota dealer meant... because my battery is obviously not an Interstate:

He meant to say that Interstate Battery Co. probably services the dealerships battery needs and maybe Interstate delivers/sells the Prius 12v Yuasa batteries to the dealership? So he thinks the batteries are made by interstate but interstate is really just a re-seller in this case.

I bet thats it.