Battery issues after Winter's Sleep...

[ACMEguy]

I tried starting up my '21 Mach after it's winter hiatus and upon opening the driver's side door I noticed that everything was dead. Looked at the battery tender and it was flashing green. Is my battery pooched or is it something to do with the BMS? Should I replace the battery? Looking for advice or shared experiences...

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[murick]

I had a same surprise about one month ago. Was able to power the car, but after an attempt to start the engine, the battery died. I did not have it on tender though, but just standing for 4 months in a parking place. The voltage on disconnected battery read 11,33 V

I did disconnect the battery and run a full charging cycle (with something called "reconditioning" phase, which is an optional phase on my charger). Then connected the battery and had it tested at a dealership, stating it was better than ever .

Few things to note:
Before disconnecting the battery you should leave the car powered down and locked for some time (read the manual). If you have a tender connected, I would probably disconnect it too.
After connecting the battery you should leave the car powered down and locked for some more time (I believe 8 hours at min). I would not connect the tender at this phase.

 

[SnowFox]

I tried starting up my '21 Mach after it's winter hiatus and upon opening the driver's side door I noticed that everything was dead. Looked at the battery tender and it was flashing green. Is my battery pooched or is it something to do with the BMS? Should I replace the battery? Looking for advice or shared experiences...

On more than one occasion a battery tender murdered my battery while telling me everything was good.

I'd say start with a new battery(most likely a battery issues or tender issue). If it's something else you'll know shortly after that. But in either case getting a new battery is probably gonna be apart of the outcome. So start there.

Side note: I never had issues with old battery tenders. They would tend everything...my snowmobiles cars, RVs....But ever since they started to add all kinds of features, algorithms, and LEDs things have gotten dicey. Probably my fault. But still more bells and whistles just brings more points of failure sometimes.

 

[BossPapa]

I had that happen once when while not on a tender and the battery was so dead my tender couldn’t charge it back up properly. Took it to Ford for possible warranty replacement and they were able to recharge it on their equipment and I’ve had no issues since. Should have your battery checked before you buy a new one.

 

[DougS550]

I tried starting up my '21 Mach after it's winter hiatus and upon opening the driver's side door I noticed that everything was dead. Looked at the battery tender and it was flashing green. Is my battery pooched or is it something to do with the BMS? Should I replace the battery? Looking for advice or shared experiences...

Sorry to hear that. Batteries in some mustangs just don't last that long while other member batteries last a long time.

 

[Optimum Performance]

You can try charging the battery out of the car, but as others have said these batteries don't like storage times. They take a dump quite often. My 2015 has only 20K on it and on its third battery because it sits too much. I honestly think it's better to pull both cables if you are putting it away for more than a month.

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