Cell #25 sagging voltage, anything to do?

gregfi · Nov 24, 2024

I have a 2017 FFE with ~55,000 miles on the odometer. I noticed what seemed to be an abrupt reduction in my range with the onset of colder weather, so I purchased the OBDLinkEX and the FORScan utility. As I more or less expected, I'm seeing all cells reporting ~4.05 volts, except of course Cell #25, which is showing 3.88 volts.

Is there anything that can be done to stop the degradation of Cell #25? The owner's manual recommends replacing the coolant and coolant filter at 10 years. I wonder if the battery coolant is failing to adequately cool Cell #25. Has anyone investigated this?

Failing that, can anyone give me a rough guess on how much longer I have before my range falls off a cliff?

Anti_Climax · Nov 24, 2024

Aged coolant isn't going to impact a specific cell. And frankly, the coolant loop on these is pretty pampered. If there's an actual cooling problem, damage to any specific cell from heat would be luck of the draw. Not even sure what you'd investigate for that - cell failures can happen at any point without an overt external trigger.

If it's sagging the options are replacing it or pulling it out and trying to recondition it individually - with no guarantee the latter would even work. Can't really estimate how the range will degrade, it will depend entirely on how the cell continues to fail. I forget the specific lower bound, but once ANY of the cells hit that minimum voltage the pack is considered discharged even if every other cell could give more.

hoprocket · Nov 25, 2024

When that started to happen to my 2018 it was roughly 3 to 4 months before I was afraid I wouldn't have enough range to get it to the dealership. But, I wasn't driving regularly every day, so your experience may be different. It will probably depend somewhat on your charging and driving habits. It seemed to get worse every time I charged which was roughly once a week or so. If your car is still under the 8 year battery warranty I'd recommend you take it in right away. If not, I'm sorry.

Sftbldad · Nov 25, 2024

You should still be under warranty!! Take it in and get a refurbished pack.

gregfi · Nov 25, 2024

It is under warranty for the next 11 months or so, but will the dealer do anything for a low voltage reading on a single cell? I'll give it a shot, I guess.

Anti_Climax · Nov 26, 2024

gregfi said:
It is under warranty for the next 11 months or so, but will the dealer do anything for a low voltage reading on a single cell? I'll give it a shot, I guess.

Their only option is replacement. These cells are not dealer serviceable. They'll get diagnostic info, contact Ford, the engineers will jerk them around for a few weeks trying to troubleshoot via email and they'll eventually give up and replace it under warranty. Question is, how long will that take and how many other bits will they try replacing first.