How to check 12v battery

welcome to priuschat, congrats on your new car! test it with the multi, in the morning before turning it on. post the result here and someone will tell you if it's good, marginal or bad. all the best!

 

If you see a black Yuasa battery back there... under the floor at the right rear of the car, use a 10mm wrench or socket to get the hold down bracket off the top of the battery. It is typically right under this hold down, in the middle of the battery, that you will see the date of manufacture... if it is 2009 or 2010 start thinking about having a set of jumper cables in the car or start looking for deals on a replacement battery in the near future. You drive enough miles per day though to let the car recharge the battery that is in there, just that as this battery possibly approaching 5 years of service, it would not be unusual for it to fail in a year or 2.

Varies from owner to owner, hot weather shortens battery life, as does draining them down too far on a regular basis. From where I sit up in the pacific northwest, you are in a hotter part of the continent. You don't know if the previous owner drained the battery to the point of needing a boost. You will find plenty of 12 volt threads in the forum to give you all the info you need... but guessing that your high mileage means downtime is a bummer as your Prius is an important part of your daily life... have a look back there and see if the battery was changed. If not bite the bullet imho.

Roland

 

The readings should be 12.9 volts on a fully charged battery with no load. I believe my battery drops to as low as about 11.5 to 11.7 volts under load, that should be the minimum. If it goes below that, you should think about getting a replacement.

SM-N900P ?

 

You might find a Scangauge II to be a worthwhile investment!

DROID4 ?

 

A $10 multi-meter might work just as good.
The Scangauge is good for lots of OTHER stuff though.

The sad truth is that you can't always tell how soon a battery might fail.
Charging it up good, letting it sit overnight and then having a load test done on it is probably the best test.
Many auto parts stores and battery shops will do a load test for free.

 

You're quite correct... ...and I should have added, I use my ScanGauge II for (1) ICE RPM, (2) Secondary Battery Voltage, (3) Traction Battery Charge/Discharge | State-of-Charge, (4) ICE Coolant temp. When I get some disposable $$, I plan to add another SG II.

 

...you're quite welcome! I should have mentioned that there's a very quick way to check the Sec. Bat. voltage which involves bringing up the main display in "Diagnose" mode (I can't remember the exact details but you should be able to find it hereabouts using the "search" function). It's fairly easy to do, and I used it before I got my SG. Good luck, and welcome to PriusChat!

 

This is what ours looks like. This was replaced by the dealer when the car was purchased (new); the car had been sitting on the lot too long, had toasted the orig battery:



And someone else here posted this pic, a while back:



If you hook up a multi-meter, either at the battery posts or at the under hood jump start point, a 100% battery will be around 12.6 volt or higher. Anything lower than 12.5 volt you want to keep an eye on. Under 12.4 volt it's days are numbered.

Addendum:

Hmm, just checked ours, it's at 12.4 volt, not so good. Hooked up my CTEK 3300, see how that does.

 

You didn't have a door open during or immediately before taking that reading, did you ??
Some stuff fires up with the drivers door and stays on for a little while.

 

I usually open the passenger door and reach across to release the hood, but this time opened drivers door, got the pressurizing response. Could be a factor, if something continues to draw power due to that. The noises were long gone.

It's been a while since I've hooked up the CTEK anyway, will see how it goes.

Thanks for the tip.

 

12.9 volts?? Maybe if you have some surface charge still left from charging it... 12.8V is more accurate if it's completely full. That said, mine has measured 12.5V since the day I got the car, and it's still working fine.

It can take a few minutes for the voltage to fully recover. The manual says to test 20 minutes after the hybrid system and all lights are turned off. So pop the hood and come back a while later to do your measurement.

Personally, I might start to pay attention around 12.2V, and get concerned below 12V (with no load - any door open, even with the interior lights turned off - causes a load). But I guess I'd rather not spend money that I don't have to, the tradeoff being that I'm more willing to risk the battery dying before I replace it. Feel free to pick your own level to get concerned based on how attached you are to your money, or how inconvenient it would be to get a jump start.