Rogue said keyfob battery low but it wasn't

[howie411]

So the other morning I tried to lock the door with the keyfob and it took a couple of presses. When I got back in the Rogue later in the afternoon it said keyfob battery low. I had to run to the store, did my shopping and got back in the Rogue. No low battery error and didn't have any issues locking/unlocking the Rogue.

I got home and decided to change the battery just in case. The odd thing was when I tested the battery I pulled out of the keyfob it was at least 80%. Grant it, its now 3 years old so probably due for a change, it just seemed odd it would stop working, then work and then show good battery life.

[VStar650CL]

How did you measure 80%? Nominal "full charge" on a lithium is 3.05V, but the discharge curve is very flat. They're near-dead at 2.95V and pretty much useless at 2.90V. If you went by 80% of 3V = 2.40V, that battery was way, way past dead.

[VStar650CL]

For those interested:

Notice in the Discharge Characteristics chart how the voltage "drops off a cliff" once the battery gets much below 3V. The 300K discharge curve is pretty close for a Nissan fob that's sitting in your pocket. Now look at the Pulse Discharge Characteristics. You can see that at the point where the constant discharge line hits 2.90V, the pulse discharge line at the bottom has literally dropped out of sight. That's representative of what happens in the fob when it tries to transmit. The moral of this story is, if you own a voltmeter, don't let your fob go much below 3V if you want healthy transmit distance.

[howie411]

Not sure the actual voltage. I just have a small battery tester that can test like 15 different battery types. It shows bars based on how good the battery is and it showed almost full.

[VStar650CL]

Then your tester may not be accurately reflecting capacity for coin cells. Compared to most other battery types, the voltage that separates a good lithium from a dead one is miniscule, so many cheap testers don't do a good job of measuring them. Check with a voltmeter. Even a $6 pocket job from Harbor Freight will tell you right away if a coin is bad, 3.0V is the magic number.

[D1dad]

I bought a multi pack online and swap them every year. My experience has been no warning, just dead.