12v battery health observation

Forget anything you've known about batteries, alternators, SOC in the past. It does no Cold Cranking. It has to have enough charge to run the computer to start the car - then once POWERED ON, the Hybrid battery keeps it going. Only in some unusual circumstances, where you might run lights, wipers, windows, blowers etc with it POWERED OFF is there much other drain - which would be rare.

- just check that it's gone back to the beginning of the YouTube.

 

All of the systems in the car do NOT shut down immediately upon "turning it off".
And some start up again just by opening the door or maybe even approaching with a FOB.
Arrange clear access to points to measure the voltage and then wait a couple of hours to check it.

IF.....the resting battery voltage never goes above 12.4 and it really is being charged when running........then your battery is marginal.

 

there's a surface charge after just shutting down. turn the headlights on for a few minutes to reduce it, then test the voltage

 

In my opinion, there is no way to get an accurate reading of your battery's voltage until a few hours after it has been running. Turning on the headlights without the car in Ready mode will probably draw down the voltage to a point less than its natural resting place, in effect a surface discharge. Either a surface charge or discharge will dissipate after a few hours. I am guessing that if you let the car rest overnight, the battery's voltage will stabilize at a level probably somewhere above 12.4 V. To get an accurate measure, though, you need to get your multimeter on the battery's terminals without the car going through its start-up routine. The easiest way to do this would be to leave the hood unlatched when shutting the car down and then approach it several hours later without the Smart Key in your pocket and measure the voltage.

 

During normal operation of the 12v aux battery, rest voltage is typically around 12.4 vdc. during charging, voltage will be around 14.0 vdc. I use a ScanGauge to monitor and particularly at outside temps in the 60's, 70s which I've found is the Prius's "happy place" with both batteries, the charge current will come down to nearly 0, and the operating voltage will reduce to 12.4 vdc.

 

Interesting observations. Which tester are you using?

I'm using a Solar BA5, so far so good at 4.5 years on an Optima, voltage an CCA both still good. Voltage might be fading a bit.

 

Not really.
Those are NOT "resting" voltages.
14.0 is charging voltage.
And 12.4 on a charged healthy battery means that a fair amount of current is being drawn.

Resting voltage is just that: no current going in or coming out.

 

Anything above 12.6v is considered fully charged. That is with the car turned off. But, there are differences in how it is measured.

I believe the owner's manual says to check the battery after driving it and allowing the car to sit for 30 minutes.

In practice, some people like to check the battery when it has been sitting cold because this is more realistic.

 

It depends on who is doing the "considering".
Technically, an AGM battery near 70 F is only about 75% charged at 12.6.

 

True, the 12.4vdc is not the batteries true "resting voltage", but in operation that's how the charging systems handles it. Indicated charge current at this point is no more than a few mils.
A good source for all the more detailed info on batteries of all types is, Basic to Advanced Battery Information from Battery University

 

IF......you are using an on-board system to tell you what the battery voltage IS......it is pretty well known that does NOT connect close enough to the battery to give an accurate reading.

And I'm pretty sure that the system is NOT designed to float the battery at 75% charge.

You have some bad input data......and have drawn a bad conclusion about it's meaning.

 

Mendel, regarding your BA5, are you able to do a CCA test from contact under hood. I consistently get a "LO" reading under the hood although the DVO meter shows 12V. I have postponed digging for the battery,
Your thoughts??

 

Well, its mathematically speaking. 6 cells per battery. 2.1 volts per cell. 12.6volts total. Granted, you can still start up with between 12.2 - 12.4 volts no problem. Lower than that I'd get a new battery.

 

No, connection is recommended to be on battery posts. I try to do that, and maybe sometimes on the clamps will work.

 

12.0 volts is half discharged or a bit less.

 

You need to update your mathematics.
AGM cells are a bit MORE than 2.1 volts per cell.