12 v battery won't hold charge

Is this is the original battery? If so, it's way past replacement time. Also, jumpstarting and running the car is not charging it properly; you would need to hook up a smart charger in the 3~4 amp range, let it run to completion. But again, if it's original battery, just get it replaced.

 

Well if it's a 9 model year old Prius?
When was the 12 volt battery last replaced?

If it hasn't been replaced? Then that's what you need. It's old enough a vehicle, and if it isn't driven much, then even if it has been replaced, it might be time for another.

Given the symptoms you describe, and the realities of aging batteries, I don't know why any competent service department would tell you the battery "should" hold the charge. Yeah...they all "should" but the truth is at some point and passage of time, all of them won't.

Even new batteries can sometimes be defective, or connecting wires loose...

I guess the biggest concern is whether you have a different problem, but my guess, and it's only a guess, is that if you can get the vehicle started after jumping it, then it is indeed the battery. Or at least that is where you should start.

 

Regardless of the age, if the 12 V battery really won't hold a charge, it needs to be replaced.
If you shop around a bit you can get a replacement battery in the range of $175.....sometimes even OEM from a dealer for that price.
If you find one for less than $150, it is probably a cheap Chinese knock-off and should be avoided.

 

Check the video that was posted a post or two down in this thread.
08 Prius Dead. 12 v battery and spare tire under Ice | PriusChat

And, read what that poster went through.

Yes, you need a new 12v. Personally, for the few extra bucks, I would buy it from the dealer. You can install yourself, the video shows you how. Or get it done at the dealer. At the dealer, for the battery plus install cost, probably around $300.

Look at the dealer Web site, sometimes they have coupons off on parts (battery) or service (installation).
Good luck.

 

I would not condemn the battery until it has been on an AGM safe , automatic charger for 24 hours. If the battery was totally dead, as it would be from non use for that long, it takes time to fully recharge the battery

 

True, sort of, but what we really need to know is how old the 12v is that is in the car. If it is a few years old, I would support Jon Hagen's message about charging.

If it is five years or past, and seeing the history of these Prius batteries -- and it is not a totally bad time for you to put in a new battery -- I would go with a new one. The peace of mind alone is worth it, especially when we are still in winter.

As you will see in the post I linked to above, a new 12v can be had for around $175-$200, a new hybrid battery is upwards of $3000. Dealer might be a little more, but you will be sure it fits.

Can batteries last longer? Sure. Just had one in my pickup that finally died after 12 years. But, I don't mind walking....even in February. If mom doesn't like taking chances, put in the new battery.

 

I agree totally, and being a bit of a tightwad, was not thinking it might be driven by someone who would not easily cope with a jump start or other.

 

I am with you. When I open my wallet, it creaks....and with my pickup, I make do, patch, turn up the radio, do whatever it takes before I spend a penny. I knew I was on borrowed time with a 12-year-old battery, but I am cheap.

HOWEVER, my wife's Prius (yes, it is wife's) is a different matter. Everything taken care of by the book. I even put out the $$$ to buy a new genuine "Toyota" lug nut from the local dealer for the Prius after I marred changing a flat tire.

My own rig, I sort through the box of nuts I have in the garage until I find one that fits.

 

$150. - $400. depending on aftermarket diy or dealer oem.

 

If you get it to start you can drive basically as far as want. If you turn it off it might not start again.

 

Maybe. It depends on exactly how BAD the battery really IS.
It would be much better to buy or borrow an external charger and leave it connected for a few hours or overnight.