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.
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.
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.