How do I charge the 12 volt battery?

Good idea, although it might be a case of closing the stable door after the horse has bolted. But time will tell if you have caught it in time.

Either connection point will work just fine. Use the one that is most convenient for you.

Have you measured the voltages (off, IG-ON and READY) with a volt meter? If so, what were they?

 

If this battery is from 2006, you should have it changed out.

 

Good idea to still buy a 12V battery charger. Buy one that doesn't exceed the 12V battery maximum charging rate; this info will be printed on the battery or available online from the manufacturer.

Make sure the charger is AGM (Absorbent Glass Mat) compatible.

 

What JC said.....

If you are fixated on charging it, I think I would be the extreme chicken and take the battery out of the car to charge it. That way you assure that you will not fry any of the Prius' electronics.

 

While his idea might sound good, it only has validity if the vehicle is not used regularly or only for short trips.

IF the measured voltage in READY is 13.5 or higher, then the odds are that the batter has reached the end if it's useful life or there is a loose connection.
The odds are very high that charging it won't help for more than a day or two.

But having a small automatic charger is a good idea just because.

And don't strain your eyes reading the fine print on the charger boxes. ALL but the cheapest Chinese imports are fully AGM compatible and most spec's stopped listing that several years back.

 

Check your Owners Manual for max recommended charging amperage. 3rd gen is 4.2 amp (2010 Owners Manual, may be slightly higher on later years). A smart charger is a "smart" choice.

Also yeah: do you have any idea how old the current battery is? If it's +4 years and giving trouble, time for a new one?

 

Time and time again, many Prius owners attempt to bypass regular maintenance and attempt to "troubleshoot and repair" in the cheapest manner possible. If the battery is over 5 years old, has ever been completely drained, and is triggering warning lights, save yourself a lot of time (and trouble) by purchasing a new one. A quick easy solution. Just check the date to verify that it has net been sitting on the shelf too long.

 

While I agree with JC that you will probably need to change out your battery, if it is still the original one, it will not hurt to give it a charge first and see how well it holds its charge.

Kris, charging a battery need not be a fixation. It, in fact, it is (or at least should be) a normal part of car maintenance - just like checking and adjusting tire pressure and changing your oil.

As long as you are using a modern smart charger, there is no need to remove the battery from the car, or even disconnect it from the car, but if you are worried about "frying your electronics" it would protect you from that. Your car, your call.

 

Obviously, I think that it is more than a good idea. Here's why. Measuring your battery's voltage standing (After being off for 12 hours and while still OFF) and under load (IG-ON) will give you an idea of its state. Without doing this you are just assuming. As the battery is not an insignificant cost, to me, it make sense (and cents) that you are replacing the battery for good reason. It only takes a few minutes to check and then you know. Otherwise you are just assuming the battery is toast. And to assume this just because it is old is dodgy because it depends on how the battery has been maintained.

Having studied the Prius charging behavior a bit, I can tell you these are not the only conclusions. If your battery shows a voltage of 13.5 V in READY state, then it could also mean that the battery is fully charged, hence the charging circuit has dropped to a float charge.

Quite possibly this is true, but without testing you will not know for sure. If it is true, charging can buy you some time so you can choose your replacement battery at leisure (or at least with less pressure) and you can change it out on your timetable. A day or two could make all the difference.

Totally agree.

I wouldn't advocate buying the cheapest of anything out of China, and while most consumer electronics are certainly built there, there is still value in buying a known brand of charger.

I have looked at quite a few battery chargers currently on the shelves, and all have specifications differentiating between flooded lead/acid and AGM/Gel.

Now on this next point ER and I disagree, but if you look up the data sheets of any AGM battery you will see that most, if not all manufacturers, state that you need to charge an AGM at a higher voltage (~14.8 V) to fully charge when compared to standard flooded lead/acid. ER posits that this is not necessary and a normal charger (13.8 - 14.2 V) will do an adequate job. While I don't disagree that this voltage will do an "adequate" job of lifting the battery's charge up, it will never fully charge an AGM battery.

So when choosing a charger for your AGM battery, choose one that will charge at the voltages as recommended by the battery manufacturer.

Also you should note that battery manufacturers recommend that their batteries be charged in various stages in different voltage/current configurations so make sure your charger can do this also. You might be able to use lesser chargers, but this will require a strict monitoring regime, lest you damage (overcharge) your AGM, which are sensitive to overcharging.

I am not going to debate ad infinitum what I have said with ER, it is quite easy for anyone who is interested in knowing what is what to verify what I have said.

 

The Optima website recommends 14.7V for "cyclic applications" and up to 15.6V for "rapid recharge". Regarding a battery charger, it suggests 13.8V - 15V, 10A maximum, for 6-12 hours.
Support - Battery Care - Charging | OPTIMABATTERIES

Exide recommends 14.8V charging voltage or less, using chargers identified as compatible for AGM/Gel batteries.
http://www.exide.com/Media/files/Downloads/TransAmer/Battery%20Care%20and%20Maintenance/Charging%20a%20Battery.pdf

Another AGM battery manufacturer (producing batteries for RVs and marine use) recommends 14.2V - 14.4V for bulk charging and 13.2V - 13.3V for float charging.
Lifeline AGM Batteries Charging Procedure

My personal practice is to use 14.4V at no more than 3A, delivered by a lab power supply. I continue charging until the current level stabilizes (it no longer declines as time passes.) In essence, this results in 3A constant current charging followed by 14.4V constant voltage charging.

Regarding the OP's original question, he can charge at either the dedicated jumpstart terminal, or at the battery itself. I personally would avoid applying more than 14.4V at either location as long as the Prius electronics remain in-circuit.

I would say that if the battery is 8 years old then it likely will not respond to charging. If the battery were so well-maintained then the OP wouldn't need a jumpstart, after all. However if he wants to waste his time trying to charge the battery, have at it.

 

I'm sorry. I didn't mean YOUR idea but the one proposed by the OP, that is that charging the battery might somehow fix his problem.
The odds are overwhelming that it won't.

And what does that second statement mean exactly ?
Are you saying that some chargers specify that they are to be used on AGM batteries and some are only for conventional flooded kinds ??

 

Are there now TWO people on here who insist that higher charging voltages are NECESSARY for AGM batteries ??
If so, neither has provided the least hint of a reference that higher charging voltages are in any way NECESSARY.

"quite easy" might be a relative term because I've done a couple of quick, cursory searches and came up with nothing of the kind.
It is indeed "quite easy" to claim anything that you want.
An actual reference would be appreciated.

 

This is what Optima has to say about charging their yellow top deep cycle AGM battery.

Support - Battery Care - Charging | OPTIMABATTERIES

 

No, they will do either AGM batteries or conventional flooded batteries. You select which type you want to charge and they charge appropriately.

 

Thank you. That is somewhat interesting but if you will notice, they repeatedly talk about "limits" and nowhere do they state that the upper end of the limits are necessary for proper operation.

Also, if you can find similar spec's for a modern flooded cell battery, I'm pretty sure that the ranges and specs would be almost identical.

Then......Optima clams that their technology is better and somehow different that everybody else's, maybe their charging spec's are different too.
(Just had to throw that in there!!)

 

So that would seem to imply that there is a switch or some other method to "select" between conventional, AGM and maybe GEL use.
Is that what you are saying ?
I don't remember seeing that kind of a switch on small chargers any more recently than about 25 years ago.
Do they really still exist.......on chargers commonly available to the public ??
(Can't imagine that it would be THAT different in NZ.)

 

My 3 year old Schumaker smart charger has a battery type selector switch. One position for conventional flooded cell, another for AGM and another for GEL, .

 

They do exist. I bought a Schumacher SSC-1500A-CA, a 3/15Amp "smart" charger, from Wrongmart in April 2014, for about $54. Amazon currently has it for $42.65. LINK Handy littler charger. Two sets of options. 1) Select charge rate of 3A or 15A. 2) Select battery type: Standard (wet or "maintenance fee"), AGM, or Gel. Once you set the options (order doesn't matter, amp then battery or battery than amp), charging starts and ends automatically.

I would have preferred to get the BatterMinder 12V AGM charger (2012-AGM), but it was more expensive ($75). However, it can charge Sealed Lead Acid batteries, which other chargers apparently can not, as none say they can.

 

Sigh.
Maybe none say that they can because they ALL CAN.

I see that it makes some of you happy to spend 3 or 4 times as much as you need to for a low capacity charger so I will quit berating you for doing that.

For the others reading this, the 2-4 amp automatic chargers available almost everywhere for about $30 will do everything that you need in most situations......for ANY type of battery and there is no selection switch to worry about.

After all, we aren't recharging a high current starting battery here. Unless it has failed completely, our "computer battery" should be able to recover enough to start with about 30 minutes on a small charger.......any type, with or without a selector switch.