Chronic low battery at scheduled service

[Tucsonjay]

Took my 19 GT in last year for maintenance in accordance with the new service schedule. The battery was found to be low, about 350A, even though it was only 15 months old. The dealer replaced it on warranty and suggested checking at the next service to rule out a system problem.

But now 2 months later the dealer finds my battery is low again. The advisor said the battery they gave me may have been on the shelf too long (?) and so they made sure the replacement was brand new this time. And so we'll check again at the next interval.

I keep the car unlocked in a detached garage with my wife's truck. I've seen recommendations here about how keeping the key fob nearby can drain the battery, but our house is at least 50 feet away. Others advise always locking the car. Would the draw from either be big enough to drain a battery that fast?

Since the first battery lasted a year and the second one only a couple of months despite no change in my behavior, I'm doubtful the key fob is the cause. And the car runs fine otherwise, with no other indication of an electrical issue.

Maybe the advisor is right when she says it may be just bad luck with crappy batteries? (Heaven knows they sure don't make them the way they used to.)

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[ORRadtech]

As I've said in another thread, new batteries should have their charge topped off when installed. Brand new batteries are never 100% charged and can indeed self discharge further just sitting on a shelf. Also, if a lead acid car battery (not a deep cycle battery) is allowed to discharge too far it will affect its ability to recover and hold a charge. Sometimes up to 25%.
If you're going to allow your car to sit unused you'd be well served to get a battery maintainer. If your garage doesn't have electricity consider a small solar panel to power the maintainer.

 

[Postal Bob]

I keep the car unlocked in a detached garage with my wife's truck. I've seen recommendations here about how keeping the key fob nearby can drain the battery, but our house is at least 50 feet away. Others advise always locking the car. Would the draw from either be big enough to drain a battery that fast?

Yes! Read this thread to get more details about keeping these cars unlocked, and/or the key fob nearby and what it does to the battery.
https://www.mustang6g.com/forums/threads/low-battery-question.229932/#post-4513825

 

[DMS]

I've read the thread referenced by Postal Bob above. It answered a number of questions I had regarding my vehicle's battery charge status / life. I keep my car on a battery maintainer when it won't be driven for a few days. In any case it is always garaged when at home, but the fob was kept nearby (I can even lock / unlock it from inside my house). Would keeping my key fob(s) in a faraday bag keep the vehicle from recognizing it as being nearby? I believe it should. Any thoughts on this?

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