12V battery - how to test it?

Nope.
I do not see how the published method is an accurate method for measuring the internal resistance of the battery, nor is it accurate for determining if the battery has any bad cells.


iPhone ?

 

I do not understand either - how the computerised Prius subsystems tests all other signals. I.e. GPS satellites signal strenght, compass indications and many others. I trust, that Toyota engineers did not install in such sophisticated car the cheap voltmeter from supermarket I agree that deeper examination (bad cells as you mentioned) of the battery requires for sure something more - but as long as the Prius is not to be used for flying (as Dreamliner I'm happy with this what I have.

 

The test procedure of the 12v Prius battery using the MFD in diagnostic mode that has been described in many threads on PC is a quick test that can easily detect a weak battery. The only significant issue is that it can be difficult to differentiate a discharged battery from one that needs to be replaced. If you take a long trip (charges the 12v battery), let your Prius rest overnight (dissipates the surface charge), and it fails the test, get a new 12v battery!

There have been many reports of Toyota dealers saying that a Prius battery is fine when in fact it will no longer hold a charge. Test it yourself.

My 12v battery lasted 8 years and over 200k miles in my Prius. That was due to never allowing a deep discharge and making mostly long trips (allows time for the Prius charging system to fully charge the battery). The Optima Yellow Top that is now in my Prius is doing well and it is likely that it will be the last 12v battery that I will need in my 2004 Prius.

JeffD (Authored the 12v Prius battery test procedure)

 

Just to get technical,, and an FYI,,

>1 There is a load test for batteries: you put a 300 Amp (or more) load on it to simulate a typical starter motor and watch the voltage drop by the second. The Prius 12 V battery, (with its little posts and cables) never sees this sort of duty. That type of load test is probably not good for it.

The 12 V Prius batt gets a ~50 Amp load for a few seconds during Boot Up of the main system while the HV battery is coming on line. Then the 12 V battery is just 'floating online' with the 12V Bus - actually this bus is at ~14.5 VDC when the DC to DC converter is supplying this 12V Bus. There is no "battery charger" in the system.
The 12V battery is what powers all the lights and radio when the car is in Accessory Mode. That and the boot up is its only job

>2 There is a capacity test for batteries: The battery is tested at its rated Ahr rating for 1 hour to see how it does meeting its rated specification. The tester cuts off at 10 VDC and displays the results in % of rated capacity.
For instance: The Prius is a 36 Ahr battery=(36 Amps for 1hr). Only the fine print says this at a 5 hr rate which means it will do 12.6 Amps for 5 hrs. (I'm making up this example, I can't remember the exact Prius spec.)

The point is, most car repair shops don't have a capacity tester. Aviation shops test batteries annually this way .
Car shops may be abusing this little battery with their big time load tester at 400 Amps or so.

 

Car Battery Testers and Electrical System Testers - Midtronics

 

Looks reasonable stuff - (thanks for the link) - hey! it's available in my country as well - just checked. Expensive though...
Being a garage owner I would equip my workshop with such tools. As for now I'm the end user only

err.. somehow I could not send this post... server error for more than 1 hour ... was afraid whether Mr Kim pushed red button

 

Tom
Good result. On checking the records for my car, the dealer (Platinum Toyota in Bath) had conditioned the battery on my car several times, but then fitted a new one prior to sale. My 2010 had been in stock for several months - but to their credit they were thorough in their pre sale service work.
Welcome to Priuschat and Prius ownership.

 

As other people have said, there is no way that little 12V battery (that floats on the 12V bus) can suck up so much current that it effects fuel mileage. If it did, you'd have a really hot stinky mess back there.

 

Actually, the 12v battery can impact MPG a bit. Our Prii use about 250 watt-hours of energy to go a mile. so if the 12v battery is pulling 5 amps continuously due to a problem on the 12v buss, it is wasting 60 watts of energy as heat.

In one hour of driving at 60 MPH the Prius goes 60 miles and uses about 1.5 kwatt-hours of motive energy. Therefore the faulty battery above that pulls 5 amps will decrease MPG by about 60/1500 or 4%. So it is reasonable that some failures of the 12v battery can cause a noticeable drop in MPG.

JeffD