Warning - Key battery low

Both fobs in car is usual case for us, never an issue.

 

What does the low battery light look like? Does it jus flash the red indicator light?

 

Don't think there is a low battery light. Just the red fob indicator would stop flashing. Also, our dash issues a warning: fob battery low, or something like that. Funny, when I've swapped batteries, the voltage on the (supposedly) dying one is still very close to 3.0 volts. And the new ones are only slightly higher. But the car seems to know the difference: warning goes away.

 

There's probably a greater difference under load (assuming you're measuring open-circuit voltage).

 

Lithium batteries (like the coin cell type) keep a nearly constant voltage through their discharge range. Once the voltage starts to drop, there's almost nothing left in the battery. That's one reason why some devices (like computers and phones) sometimes have a hard time judging how full the battery is; it's hard to know by voltage alone. Alkaline batteries drop fairly linearly across their whole range.

Also, the load on the key fob should be so low that the voltage drop should be pretty negligible almost all the time - but perhaps when it's transmitting. Radio signals require a lot of power.

 

See below for 2012 prius

 

Just a word of warning. I discovered after replacing the battery in my "main" fob, that it started giving me the low battery warning again just a week or two later. It turned out that particular fob was draining the battery excessively (I measured the voltage on the fob with battery installed, and it was dropping noticeably during the course of a day). I switched to my 2nd fob, and that one has been working fine for 6 months. I still have the bad fob as a backup, but somehow, these things can have electrical issues.

 

That's a bugger, wonder how it happens? Maybe a short right where the battery sits, allowing electrons to short circuit between the two faces??

 

Just came across this.. It was giving me a warning for about two months. For the past week a warning would pop up every time I would sit in a car. Today, I could not open the door.. I had to use the key to get in and start the car. I've no idea if that battery completely died since I still was able to start the car, but that was enough to go and buy the battery. That particular battery is tough to find. Neither Walmart or Walgreens had it. Took the last one from Autozone.

 

Easy to find on-line, and much much less expensive, in a variety of brands. Radio Shack has it, or at least used to have.

 

Good job for using up every last drop of battery and not wasting resources or money. The battery is indeed dead. The NFC used to start the car gets powered by the start button. The FOB doesn't need any battery for this function.

 

Amazon 10 pack or Ebay 10 packs are cheap. Buy the cheapest name brand. Got Sony for myself.

 

yes, but you get old stock, poor quality, or counterfeit. i went that route and don't recommend.

 

I never got old stock. Most ads show the expiration date and the ones they shipped exceeded that date greatly. Also do not buy off brands. Sony, Panasonic, etc are great brands. Have several of each size for my stash and some are 10 years old and work great.
Freshly Expire 2025 5 Pcs x Sony CR2032 Lithium Battery 3V US Seller | eBay
4 New Sony CR2032 3V Lithium Coin Battery Expire 2025 Freshly New USA Seller | eBay
5 PC Sony CR1632 3 Volt Lithium Button Cell Battery USA SHIP | eBay

Shop and compare at several sites.

 

But I don't need 10 pack, I needed only 1.

 

I have always got my battery's at Walgreens drug store.
They were in a two pack.
One for a spare or replace both at the same time.

 

PM me your address. I'll send you one from the pack I bought on Amazon. It'll probably die before I need to use it, anyway.

 

Have the same problem, buying razors at Costco...

 

I get this message all the time. For me it has been a meaningless message. The car lights up at my approach and everything always works but the message is always there when I turn the car off. I have replaced the battery three times since 2012 because of the message though there did not seem to be any problem with the key battery and I would ignore the message for quite a while before replacing the battery to get rid of the message. I now ignore the message because it appears to be meaningless. I have had the message appearing for over 6 months now. I want to disable the message. Is that possible?

 

odd, i've never had the message, and still on original batteries.