12 Volt Battery

don't know if this will work, but have you seen this thread:

http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html

 

Getting at the battery itself only takes a minute. Then you an test it with a multimeter. You open the access to the storage for the charging cord, then you lift off the small cover in the right rear corner of the cargo area, then you lift off the storage tray which is just under that. The 12v battery is exposed and easily accessed.

I have permanently connected a Battery Tender. I occasionally plug it in. When the light turns green, I know the 12v battery is fully charged.

 

Andy, I also have owned a Prius for six years. The PiP 12v battery is MUCH easier to access than earlier models. I was not exaggerating when I said it takes only a minute. It is as easy or simpler than accessing the front fuse box. You could do it in front of a salesman with a minimum of disruption.

 

Yes! it has been moved in the plug-in to the right rear really easy to see and check!

 

And you feel the need to test the battery before you have even bought the car why?

Seriously, get the car home for at least a few months before you worry about this, it should be fine for at least 2 years anyhow.

 

I have verified this procedure for checking the 12v Battery Voltage in my PiP Advanced:

1. Foot off Brake Pedal
2. Push POWER Button twice
3. Hold in INFO button on right of NAV display while doing next step.
4. Turn Headlights On and Off three times. - Menu comes up.
5. Press "Function Check/Settings" on NAV display.
6. Press "Vehicle Signal" on NAV display.
Battery Voltage is displayed - mine said 12.2V
7. Place Foot on Brake Pedal and Press POWER button turning on the car.
8. My Battery Voltage then said 14.4V.
9. Press POWER button to turn off car.

 

One thing that I would add to jbrad4 is on your first check with the Service Menu is to check with a voltmeter right at the battery terminals.

On my car the Service Menu reads 0.7V lower than with a voltmeter right at the battery terminals. This could make a big difference in determining a good battery from a bad battery.

 

OK jbrad4. Where in the "heck" did you find that nugget of information? That is a beautiful thing. Are the steps the same for the "base" model? I will give it a go when I get home.

 

Thanks Jbrad!
This belongs in a Sticky!

Don't Mess with Texas!

 

Remember that when you start the car, the voltage reading is the charging level not the voltage of the 12v battery. The 12v battery is charged by the traction battery when the car is in "READY".

This is an interesting process but checking the voltage at the battery is just as simple and is more direct.

 

Because of http://priuschat.com/forums/gen-ii-prius-technical-discussion/100011-closed-minds.html, which interestingly enough was posted by the OP here...

 

It's always been in the the right rear of the Gen 2 and 3.

I forgot to look at the 12 volt battery placement in the PiP, but when I've looked at the back of Gen 3s, there's a LOT less stuff in the way of the 12 volt on the Gen 3 vs. Gen 2. Changing the 12 volt on the Gen 3 looks a LOT easier. (Did it myself on my Gen 2.)

 

Very good point!

 

I and several others have compared the voltage shown in the service menu (though not always on a Plug-in, the systems are probably very similar, if not identical). The voltages can vary quite a bit at the battery compared to what the service menu shows. In my case, the service menu showed 11.5V while the battery measured 12.2V.

Also keep in mind that the battery is under a load of probably 10 Amps or so to power the various computers. Every place that tells you to judge battery charge by voltage will (or should) also tell you that the battery must be unloaded, and be at rest for probably at least an hour or so before you measure the voltage for an accurate result.

Even just opening the trunk to access the battery will put it under a load (for the various interior lights, and computers for the SKS and other systems, even if all the lights are turned off). Popping the trunk, you'll probably have to open the driver's door, which runs the pump to pressurize the brake system.

So to get an accurate result, I suggest you sleep overnight in the back of the Prius with a multimeter. Have a family member lock you inside, and take the key fob with them. When you wake up in the morning, you can dig into the battery compartment and measure the voltage to get a good reading.