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Can anyone help me w/this? I put a new battery in, it works well, but w/in a month or so the car thinks it is low battery and at that point it'll not work some of the time. Not long later it'll not work a lot of the time. I put another new battery in and it works well for a month or so again. My multimeter shows the battery has about 3v, so it is only about 10% drained. This happens w/both these OEM key fobs and different brand batteries.

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  • Welcome to Motor Vehicle Maintenance & Repair! May 18, 2023 at 15:12
  • Is this a "smart key" versus where only button presses do anything? May 18, 2023 at 15:14
  • Yes, Paulster2. May 25, 2023 at 12:35
  • A smart key has two way communications with the car. The car interrogates and the fob responds. It could be there is something which is sending out a signal which is like the car, but not the car, and the fob is continually responding. This could burn up the battery in short order depending on how often it's getting pinged. May 25, 2023 at 13:39

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A measurement reading 3.00 volts when not in use (i.e., "open circuit) means that the battery has roughly 10% of life remaining. A new battery should measure about 3.3 volts. The discharge curve is very flat, so it's not possible to get an accurate estimate of remaining life based on open circuit voltage.

See if you can measure battery voltage while in use -- while the fob is transmitting. You may have to monkey around with a short piece of wire to access the hidden side of the battery while you press the fob's button. I think you'll see that the voltage of your battery falls under 3 volts as soon as you press the button, leading to the low battery warning. A fresh battery remains well above 3 volts while in use. This method -- testing voltage while in use -- is the only accurate way to learn if the battery is good or not.

It's commonplace for third-party sellers at a famous online merchant to sell counterfeit and / or nearly dead lithium coin cells for significantly lower prices than average market price. You may have been snookered if you buy your batteries online. As an experiment, you can try paying full retail price for a battery at an established national retail chain store. You can be fairly certain that their batteries are real.

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  • Ty. So, I bought new batteries, but though they didn't show "low battery" on the car, these were initially sometimes not being recognized by the car (this happens w/low batteries a lot). Anyway, the new (used a few days) one showed as 2.78 during use, 2.8 immediately after use, and 3.01 when not in use for a while. amazon.com/dp/… is the purchase location, and a ton of good reviews, plus the package shows 3/26 best before date. May 23, 2023 at 22:41
  • I opened another battery in that package in case it was just a bad cell. It shows: before use 3.3, 2.8 in use, 2.87 immediately after use. What do you make of this battery? For an experiment, Amazon Basics sold by Amazon should be a good test, I'd then think. May 23, 2023 at 22:51
  • @SamSchaperow Right, the seller sent you nearly-dead batteries as 816 customers reported. Some of the positive reviews likely came from bots or shills, SOP for Amazon 3rd party sellers. Notice the 3 year shelf life? Normal shelf life is 10 years on lithium button. They're selling 7 year old batteries. That's why they're so cheap. See words "as an experiment" above. You'll need to go to a brick and mortar store. (Eek!) Amazon Basics? Who knows?
    – MTA
    May 23, 2023 at 23:04
  • Why should 7-year-old batteries that are not expired be drained? Unopened batteries that are not expired, shouldn't they still be in good condition? By the way, my multimeter for battery testing seems to work well with AA batteries, so why do I have to check these kinds of batteries while in use but not AAs? May 25, 2023 at 12:39
  • @SamSchaperow It's not a perfect world. Sellers lie. So do manufacturers. You bought junk. Get over it. Wishful thinking will not turn junk to quality. You have a solution, stated above. Buy name brand batteries from a trusted brick and mortar store with an 8-10 year shelf life and your key fob will work.
    – MTA
    May 25, 2023 at 13:25
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The Amazon Basics batteries arrived with an exp. date of '30. Measuring the battery's power immediately after use, it shows like 3.29, while the other batteries showed like 2.8. Ty to all who gave recommendations!
Sam P.S. I returned the other batteries and have learned my lesson to only buy batteries of these types with an exp. date that's close to the 10 year mark.

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