12V battery measurements after 44 months in service. Replace or not yet?

No.
Don't leave a battery on a charger overnight. Thats very bad for it.
It will continue to input to the battery even after the battery is fully charged.
Which will over charge the battery and boil the electrolyte.
Even a battery thats a few volts low will charge up to its max very quickly. In less than 20 minutes usually. After that further charging is unneccesary & harmful.

Your standard battery charger is a dumb brute force charger. It is not smart. It will continue to output voltage to the battery until you unplug it.

There's not much you can do with a standard battery charger after that particular battery has reached its maximum charge. After that its just damage.

Now having said that there are some chargers that have an anti sulphating mode that pulses dc to the battery to help desulphate the battery but thats out of the scope of this post.

A float charger on the other hand is smart and has a circuit in it that will detect when the battery is full and shut off.
A float is designed to work on a fully charged battery. Then over time usually in storage it will detect any loss of voltage during storage below 12 volts and turn on and supply a very small charging current until the battery is fully charged again and then it turns off.
A flaot charger usually uses a small 500mA wall wart for its power source.There is no fire hazard as the current involved is very small.

A float charger is usually used with car's, motorcyles, snow machines, or boats being stored.

Its a great thing to put your Prius battery on a charger once a week for 10 minutes. Its an excellent thing to put your Prius battery on a float charger if your gone more than a week. Especially if its very cold in the storage unit.

 

Hi Ed,

I disagree with this assertion. Here are a couple of recent examples:

1. My HiHy battery is one year old. (The physical size of the battery is the same as the 2G Smart Prius, although the battery is flooded lead acid.) Two days ago, I measured its voltage at 12.2V. I connected a lab power supply set at 14.7V, to the battery to charge it up. It took an entire day for the charging current to drop down to ~20 mA, which is the level that you would expect when the battery is fully charged.

2. My Ford Mustang battery is five years old and is physically larger than the HiHy battery, with 540 CCA rating. I measured its voltage at 12.1V a couple of days ago. I connected another lab power supply at 14.7V to charge the battery up. After 1-1/2 days, the charging current is still ~0.6A. (That battery is clearly marginal, but it still starts the car without a problem.)

I would say that 14.7V is a higher voltage than most battery chargers will provide at the 10A setting. My battery charger which is ~20 years old will only provide 13.8V when set to the 10A range and charging those batteries. This is why I'm using the lab power supplies instead.

Therefore, I would not expect that 20 minutes of charging time would be particularly helpful in changing the battery's SOC.

Many auto owners think that the 12V automobile battery will quickly recharge, but this is untrue. Consider the Prius 2G Smart 12V battery with a ~35 Ah rating. Suppose the battery is 50% discharged: then it will take at least 17 hours at an average charging current of 1 A for the battery to recover its charge. Typically, the charging current starts at 3A or more, then the current flow decreases as the battery charge starts to recover. In addition, there are heat losses and other inefficiencies involved, so even more time is required.

 

I don't work for them or receive money from them, but have used their products for 8 years now

BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) | All | Battery Chargers by BatteryMINDers.com

They work well. However, the maintainer is NOT capable of charging a dead battery. You need a regular charger for that

 

My statement was based on a healthy battery that saw a very recent discharge. I think all the batteries you have used as an example may not be 100% healthy. And I should not have used "a few volts" either. Thats a little too much to expect. I agree with that. May I retract that and say a volt on a very good battery with a charge time of a few hours.
But not overnight in any case was my point just poorly written.

And I was trying to make the difference between a charger and a float. 2 very different animals and misuse of the charger can make your battery much worse.

 

Which is why I have two separate chargers. The float charger for "top up" maintenance and to extend battery life, and a "real" automatic battery charger to charge a mostly dead battery

 

Sorry I may have missed earlier posts. How and where do you measure the voltage and what load do you put on the battery when it read 11.9V? Thanks!

 

Couple questions, isn't the 13.8 v. just about ideal for charging the 12v, as that is very close to what the car does? And does the Prius float charging system taper down as 12v. battery charge builds? I thought it was said otherwise before, on the board, about the tapering charge.

 

Yes 13.8 is exactly whats needed. And as Jayman confirmed a charger and a float are 2 very different animals.

A charger is unique in that it will supply alot of current whenever its needed. It will supply the big inital charge and then slowly charge the battery, time wise depending on the battery health, age, and temperature. But does not shut off. Batteries do not like constant input after they have become charged. It tends to overheat the electrolyte.

A float does one thing. It maintains the battery. It is designed to be used on fully charged battery. It will struggle on anything less than a charged battery. It will struggle on a marginal battery, one which has seen a few heavy dischages which usually begins sulphation.
When the battery is back at fully charged a float shuts off.

Using a float charger on a stored battery is the best thing you can do to extend battery life. It is foolproof and battery likes being fully charged all the time.

They sell a chemical you can add to the cells of a battery to fight an aged battery with sulphation but most batteries are sealed.

They make a charger with desulphation mode which pulses the dc charge.

 

I believe you are asking why I used 14.7V to charge the flooded lead acid batteries on my HiHy and Mustang. The reason is that I wanted to speed up the charging process. Higher charging voltages are acceptable when the ambient temps are low. It has been in the 40+ degree F range here recently.

It is true that 13.8V is the voltage found on the Prius 12V bus when the car is READY, so you will be very safe using that as a charging voltage on the Prius 12V battery.

The 12V bus voltage is supposed to adjust downwards slightly as the battery reaches full charge, but I have not noticed that happening.

I set up my lab power supply at 13.8V to charge up the one-year-old battery on my 2004, yesterday afternoon at 4 PM. IG-OFF voltage was measured at 12.6. When I first powered up the power supply, the current flow was 3.18A (current-limited by the capacity of the power supply). After a few minutes the flow dropped below 3A so that the power supply was voltage-limited at 13.8V.

I checked the current flow over the course of the evening, and by 10 PM it had dropped down to around 0.8A. By 7 AM this morning the current flow was 60 mA (of which 20 mA is quiescent current drawn by the ECUs), so I decided to declare victory and turned off the power supply.

This provides another example of why I say that overnight (at minimum) charging is required if the 12V battery is low. My battery started at around 75% SOC given a voltage reading of 12.6V (since new fully-charged is 12.9V.) Obviously, if the battery started at a lower SOC then even more charging time would be required given a 13.8V charging voltage.

 

I noticed you had the 13.8 v charger 20 years old is all, as I have something like that, but nothing else, and I am not in the mood to buy new things. That's the reason I asked.

I still don't understand what is going on with the charging system in the car. My car usually sits most of the week unused, and then is driven on the weekends, usually say a couple 2 hour trips. So in that case, I don't see how my battery is maintaining charge, but it must have after this time. Mine is nearing 4 yrs old, and is the white GS one, even though I have smart key and backup, but no navi. I see the volatge is lower this winter, 11.9 etc ig-on, but still functions alright.

My purpose is to solve this problem of discharging over time, and extend my batteries life, new one or old one. I would like to use my Schumacher auto charger with a 2 amp setting, but don't know if that would be OK. I also would like a way just to plug something in in the driveway, so later it is easy to disconnect and go.

I also would rarther not go through the system signal check process so often,once in a while when there is time, OK, but not every other day. I want to get in and go, and use the car as needed, not just drive to charge the 12v. battery.

Thanks.

 

Yes I have seen report of the tapering behavior of the 12V bus. My battery seems weak but it still shows a bit of tapering. See graph below of the 12V bus values recorded during 4 trips. After 10 days of non driving with the SKS left on, the first drive (blue data curve) had the highest initial charging voltage and largest tapering effect. As the battery gets charged back up during each drive the initial voltage became lower and the tapering effect smaller.

 

That would be OK. For that matter it would be OK to use the charger with the 10A setting, because in fact the charger will only be charging at 4A or less, based upon my experience. I have the same make charger, with 2A/10A/50A selections.

The reason that I am using my lab power supplies instead of the charger for 12V battery charging purposes is because I think my charger takes too long to charge up the battery. The charger starts pulsing the charge much sooner than I think is appropriate.

 

Here are measurements on the one-year-old battery in my 2004, taken this afternoon at the dedicated positive jumpstart terminal, using my Fluke 87 DMM. The car was driven 12 miles earlier today and the battery was fully charged last night. Ambient temp is currently 62 degrees F.

12.7V, IG-OFF
12.5V, ACC-ON
12.2V, IG-ON

Your IG-ON voltage is a bit low but I assume that your ambient temp is quite a bit lower, and the battery will produce less voltage under load, given those conditions. How many miles has the car been driven since the new battery was installed? If the car hasn't had much use, then the battery may have experienced some discharging since it was installed, and it may not have been fully charged at the time of installation.

 

I experience nothing like your seeing. When I hook my charger to my 3 year old agm it pulls 3 to 4 amps for maybe 5 minutes then very quickly drops to 0 current draw within a 1/2 an hour.
The monster battery in my Crown Vic reacts the same. Its a good sign of a healthy battery. Pulls major current in the beginning and then tops off quite quickly.
The longer it takes to charge the more unhealthy it is. Unless your current limiting the charge especially in the very beginning.

 

Hi Ed,

It's hard to respond to your observation without knowing what SOC your battery started at. However, I assume that the starting SOC must be pretty high given your findings.

What does "0 current draw" mean? What is your means to measure charging current? Can you measure charging current when it is less than 0.5A?

Here is one article that indicates charging time for a lead acid battery may be up to 36 hours for larger-capacity batteries, depending upon the charging protocol used. It also indicates that charging current should eventually decline to 40 mA with a good auto battery.
Charging the lead-acid battery

Consider that the 2G w/Smart 12V battery is rated at ~35 Ah. I would assume that if an owner has a starting problem, that battery is drained so that its SOC is no greater than 25%. Therefore, at least 27Ah has to be replenished. If the charging current was an average 3A, then at least 9 hours would be required - even more, given the inefficiencies associated with the charging process. However, the reality is that the charging current will start off at a relatively large number but then will drop off after a while, as you have also observed. Therefore, an even greater amount of time would be needed to bring that battery back to 100%.

 

Hi there,

If fully charged is 12.9 then a 75% SOC as you say above should be 9.65 volts. Your battery was at 12.6 which by my calculations is 98% charged. Running it on a charger for 15 hours to put 3/10's of a volt in it doesn't make alot of sense to me. My float can do that.

And somewhere along that 15 hours it will reach peak charging and not need any more charge. But your dumb charger will keep giving it input until you shut it off. Not good for the plates, case or electrolyte or your electric bill.

All I'm saying is for good battery life a quick charge on a quality charger once in a while till the ammeter shows 0 current draw is quite sufficient for long battery life. A healthy battery will take 20 mintues to do that cycle. If your nutty about your car battery and insist on a 100% charge which really doesn't matter by the way because the second you put a load on it those 3/10's of a volt will disappear, then put a float on it and forget about it. It will take 20 hours to put those last 3/10's in.

So we disagree on this basic issue. It doesn't mean I don't respect your opinion on anything else you post about and I do enjoy our discussions. Peace.