Discharged 12V battery recovery advice sought

i don't know about charging, but the optima should be able to handle deep discharges with more gusto than the oem.

 

If you can get it going after charging, drive it for a day or two before checking voltage, with a digital multimeter. At the jump start point is fine. If it's 100% (which is dubious) it'll be reading 12.6 volt or more. 12.5 is borderline, 12.4, best replace.

With the OEM batteries, they caution to keep charging rate under 4 amp. Not sure about what you've got though. An intelligent, sub-4 amp charger, hooked up at least overnight, with status lights, is a good course.

 

Best bet is to beg/ borrow/ buy a smart charger designed for sealed AGM batteries. If you use the larger "dumb" charger at the high charge rate for too long, you risk boiling away some of the valve regulated AGM batteries limited amount of electrolyte. Boil too much of that away and the battery is scrap. The other side of that is that the sooner you get that battery back to full charge, the less sulfation damage you will have.
I have A few Optima red tops and a dozen or more of the Exide Orbital spiral cell AGM batteries that are a clone of the Optima.
I use a Shumaker SC-8020A smart charger for main charging dutys, The schumaker has both smart charger and desulfator functions and is safe for AGM batteries. I use BatteryMINDer 12117 battery maintainers, which will safetly desulfate / charge and maintain any type battery including Optima yellow top batteries.
When the snow gets deep in our North Dakota winters, I often park my Prius for several weeks to several months. The Prius has more "always on " electronics than most cars, so will discharge the 12V battery to damaging levels in a couple weeks.
If my Prius is not to be driven for 2 weeks or more, I plug in the BatteryMINDer 12117 I have in the storage box below the rear floor, to the battery (using the optional direct to the battery ring terminal harness) and leave it connected to an extension cord. The BatteryMINDer's 1.3 amps is enough to power the parasitic drain of the Prius while maintaining the battery at full charge and free of sulfation.

 

1. I understand that the Optima will accept up to 10A charging current without a problem. I therefore suggest that you revert to the 6A position on your charger.
2. Continue to watch the voltage and current measurements on your charger as the battery continues to accept charge. When the charging current starts to decline from 6A, what is the volts reading at that point?
3. Does the volts reading remain constant as the charging current declines further? (It should.)
4. See what the charging voltage and charging current is, at the point that the charger thinks the battery is fully-charged.
5. Regarding how to assess the battery's condition via voltage measurement, wait at least 8 hours after the battery charger has been disconnected, to measure voltage across the battery. A fully-charged AGM battery should measure 12.9V or better.
6. Depending upon your results for 4 and 5 above, if they are not satisfactory, one reason may be that you need a 12V charger intended for use with AGM batteries.

 

I think Patrick pretty much covered everything that is needed to be known concerning the OP's question. I cannot or would not add or detract any of the above information and I furthermore agree with what was said in all of the details.

I could not have worded it better myself.

 

Oh, Ron, come on. Not even a little bit....

Having said that, whenever either of you give advice it is terrific. And the couple of times I have ignored it, I paid the price....

I've learned my lesson with you two -- and actually about 20 or so others who are fantastic on this board...

 

archae86,

Optima Battery 38 Amp/Hr rating

Theoretically, applying 6 amps for six hours would just about fill up a battery. However batteries tend to waste electricity when they recharge. Since you are seeing that the amperage on the meter is declining it would be logical to think that the charger you are using is a "automatic" charger.

Unless your voltage while charging rises above 15 volts WHILE charging, I don't think you will overcharge the Optima. Be aware that it is not uncommon to see voltages in the 14 volt range when charging a battery. Remember the Prius normally reads about 13.8 to 14.2 when running the MFD test that a lot of us here on PC use.

I would leave it on 6A for the duration. I bet it will be fully charged or very close to it by the time the late news comes on tonight. If you switch back over to 2A, it is just going to take longer for the battery to charge.

Best of luck to you.

Ron (dorunron)

 

Sounds good. 15V charging voltage (if an accurate reading) is too high. 14.4V is the most I would charge the battery at.

The good news is that your charging current is declining nicely. Hopefully you'll find that your battery holds the charge and you will be back to status-quo.

 

Honestly, I think your battery is "charged" enough at this point for the Prius to take care of it from here. It won't hurt to run it on the 2 amp setting until the late news comes on, which should be another two hours from now if I understand the way the time zone's work.

You might want to invest in a good smart charger for your Prius. However the charger you have is wonderful for when the voltage is as low as yours was. A lot of the smart charger's today won't start up if the voltage is that low. The work around in a situation like that is to hook up a battery in parallel to the battery needing charged. This fools the charger into thinking that enough voltage is present and will begin to charge the battery. I have used portable start packs to do this and have had no problems working with severely discharged batteries such as your was.

If you do invest in a charger, get one that has a setting for AGM on it. That will give you the correct charging parameters that are normally used when charging or recharging the battery for the Prius. I use a BatteryMinder 12248 and run it on the 4 amp setting. Lots of folks here on PC recommend the CTEK brand also.

For reference sake the 15 volt figure I used above would indicate a over charge situation. That is why I said what I said, but I should have been more clear about it. The parameters that the charger I use limits the voltage to 14.6 volts for the AGM type battery, 14.4 for flooded type batteries as well as 14.1 for gel type batteries.

But it does sound like you old timer battery charger is doing the job. I am aware that it is the old one you mentioned earlier in the string.

Hope the Optima holds the charge once you get it back up to normal voltage. Best of luck to you!

Ron (dorunron)

 

All sounds good.

Since you have all these DMM, it sounds like you are an electronics enthusiast. If that is the case, and if you have a lab power supply lying around, please note that works very well as a 12V battery charger.

Just set the voltage to 14.4V or 14.6V and set the current to 4A or less, and then let the power supply work as a 4A constant current supply which will eventually move to a 14.4V constant voltage supply. Then you don't have to worry about exceeding the voltage and current charging parameters.

 

The Optima should not have been harmed by this event as this is what the makers say it was designed to cope with. AGM batteries generally cope well in this situation provided they are charged immediately "as in your case" that they become discharged.

John (Britprius)

 

Good job, your monitoring and adjustments provided the smarts to make an old "dumb" charger recharge that AGM battery without overcharging it.

For me, the Valve regulated spiral cell AGM batteries made by Optima and Exide Orbital have been so very reliable in starting applications, many working well for 15-20 years. One Front drive loader tractor I built, had a new red top Optima installed at that time, 21 years ago. That battery still starts the tractor's 305 Chevy every day.
They are so tough and reliable when treated well, yet so easy to destroy if abused.. Connecting a big "dumb" charger to an AGM battery, set the charging rate at 40 amps and walk away from it for half a day is a sure way to dry out and destroy the battery. With a "smart " charger designed to charge an AGM battery, connect it and walk away. The charger will fully recharge the battery without overheating it or drying it out.

While an unregulated "dumb charger will have the amperage taper off as the battery reaches full charge, often the voltage will rise to the 15-16 volt range if you leave them connected when the battery is fully charged.

 

The crappy little battery in the Prius does not last forever. I have installed a few already. There is not much to do but drive the car and see if the battery is shot or test and replace the battery.
I carry a compact set of jumper cables in the under cargo compartment just in case. The upshot is the Prius is a great car to leave "running " while waiting for something, the ac and heat works and the engine only runs occasionally.