Gen III 12V Battery Normal Range ?

lower end voltage depends on the situation. AC voltage should be no lower than 10.5 actually. granted that is low, another thing you will want to look at is what the voltage reading is 30 minutes after a drive of more than 15 minutes.

while driving your battery should be at 13.5 to 14.4 volts. (varies by temperature and condition of battery)

you will experience "float" charge if you check voltage immediately after its been driven which is why you want to wait 30 minutes minimum. an hour would be better.

for this measurement, you want it to be 12.5 to 13.2 volts.

P.S. with ACC on, its NOT unusual to see the voltage readings you are seeing. even if nothing appears to be on, the switch engaging the traction battery must be held in place so power is going to that from the 12 volt battery is always on.

 

Dwight....

What's the Service Menu Screen???
Is this related to something your connecting to the computer?

Bob

 

About the only way you will know the condition of the 12V battery is to have it "load tested". That should give you warning of impending failure.
A fully charged 12V battery should be about 13V under no load, but I have seen batteries that will measure 13V under no load, but when even a small load is put on them, the voltage drops dramatically.
Most automotive parts places will load test a battery for free, but of course their objective is to sell a battery.

 

load tests can be done without taking it anywhere. drive the car to charge battery up. then park it, wait an hour. test voltage. should be 13.2-13.5 volts

then put car in ACC mode and turn on everything

defrost, radio, headlights. that should give you a good indication of where you stand.

a good battery will be between 11.5 to 12.5 volts

 

yes except the 12.4 volts with nothing on seems a bit low. the standing voltage is dependent upon battery condition and temperature. what was the temperature? must have been relatively chilly. 12.4 is a bit lower than it should be. i will check mine, and right now its in the low 40's i think well, hold on, brb...
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ok, back...way off on my estimates... its 30º out. and checked the 2010 was 12.7 volts, driven last about 8 PM last night. the 2006 was 12.4, driven last about 4.30 PM last night

your 12 volt battery is actually 6 2.2 volt cells. on my Zenn, the general level for major concern is actually 9.5 volts. going below this level, you run a high risk of polarity reversal of a cell. if that happens, your battery is officially comatose. doesnt mean its dead but does mean its life as a reliable source of power has ended.

 

I know it is 12 years old tread but may be helpful for any reader in the world who google things about the Prius 12V battery.
My battery is 6 years old now, I have 3rd gen Prius powertrain.
Since 2 years ago it is at 12.4-12.6V after 1 hour or more READY mode with ACC mode, IGN OFF.
With IGN ON, 2x power buttons, it is at 11.7-11.9V
Headlights ON, 2x55Watts, voltage drop to 11.1-11.4 V
It never fails to start the car to READY mode even with the Smart Keys system.

So far it is in good condition although not new. There is a saturated region after 3-4 years when the open voltage at about 12.4-12.6 V full charge. The main important part is it holds the voltage above a minimum of 10V when it starts the car at 60A load to bring it to READY mode. Unfortunately, we cannot really predict that point.

My current method is to press the power button 2x (IGN ON) and if the Voltage is still above 11V for 1 minute, it is still decent. My old dying batteries in 2nd Gen always go below 11V when IGN ON.

 

What is ACC mode? How many times should I push the button? (Sorry, I'm a n00b)

 

if you don't get a reply, it should be in the o/m

 

ACC 1X press, IGN ON 2x, without pressing the brake. In a normal car the limit of voltage drop is 9.5V during starting, in hybrid, 10V when you start to Ready mode. A usable battery should be above 12.2V open voltage, no load after fully charged. Generally speaking, if the battery is discharged, 11.8V no load is the limit before permanent damage on battery started.
The easiest way is put the car to Ready mode for 30 minutes once a month if you don't drive more than 30 mins in a month. It charges both batteries