Low battery question

[2021CSGTJH12]

Hey guys. I have a 2021 Mustang GT convertible. It has 7100 miles and brand new battery I got 4 weeks ago (Die hard). I usually drive short distance once or twice a day. This is the longest I’ve gone about five days since I driven this car. I tried to start and he struggled to start, but it did start.

Sidenote: because this car has an alarm and it’s very sensitive I will leave the key 2 feet from the car in my garage hanging on the wall. The car does not get locked.

(1) because of the statement I said above or that have some type of drainage since the car does not go to sleep if the key is next to it or does the car go to sleep?


(2) I assume the battery is low so “MYMODE” doesn’t show up and all the setting went back to factory color. Does this happen when battery is low?

Thanks

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[ORRadtech]

I don't believe that the car will go completely to sleep if a fob is that close.
I don't know if the mymode is a given with a low battery but modern cars do very, very odd things when the battery gets low.
I think the easiest thing for you is to buy a small battery maintainer and just hook it up when the car is sitting.
We have a '12 Edge we use as a spare car. The battery doesn't go flat in five days but it's also locked with the keys far away and has far fewer electronic controls than even my '18 convertible. It lives on a maintainer and is always ready to go.

 

[Postal Bob]

Leaving the car unlocked, and the key fob near the car, will drain the battery very quickly.
As an example, my car is always locked, always on a battery tender, and the key fob far away from it. If my car isn't started for 2 weeks, it goes into deep sleep mode to conserve the battery, Recently I had my car at my detail shop for storage when I was getting a new driveway put in. 4 days after dropping it off, I got the message on my FordPass app, that the car was going into deep sleep mode because the battery charge level was getting too low. When I called the shop, they said they normally keep the cars unlocked, and the key fob on the windshield. I had to tell them they can't do that as it drains the battery quickly. I told them to lock it, move the key fob away from the car, and put a charger on the battery.

 

[2021CSGTJH12]

Leaving the car unlocked, and the key fob near the car, will drain the battery very quickly.
As an example, my car is always locked, always on a battery tender, and the key fob far away from it. If my car isn't started for 2 weeks, it goes into deep sleep mode to conserve the battery, Recently I had my car at my detail shop for storage when I was getting a new driveway put in. 4 days after dropping it off, I got the message on my FordPass app, that the car was going into deep sleep mode because the battery charge level was getting too low. When I called the shop, they said they normally keep the cars unlocked, and the key fob on the windshield. I had to tell them they can't do that as it drains the battery quickly. I told them to lock it, move the key fob away from the car, and put a charger on the battery.

Wow! Thank you for this detailed response. I never knew about this. I had a 2003 Mustang GT and always kept my key on the windshield in my garage when parked. But that car has almost no computers lol. So I did the same. I am hoping there is no electrical draws I don’t know of and just my operator stupidity.

I was able to find a BATTERY VOLTAGE on my Mustang and it read 9.5!!! That’s low but I was able to start it every time.

 

[Skye]

Given the conditions (fob nearby+vehicle unlocked+short trips), yes, the battery will drain quickly.

If the alarm is overly sensitive, it isn't effective. I'd look into fixing that. If a Ford product, the dealer could support. If an aftermarket piece, I'd search for a local repair, alarm or audio shop that could help.

The fob should be physically secured somewhere, not left in the immediate vicinity of the vehicle.

To prevent relay attacks and battery drains, the fobs should be placed in Faraday pouches. Multiple vendors sell different styles. Google "faraday pouch" and you'll see several. My most recent set, I purchased from this company:

https://shop.faradaydefense.com/

The vehicle should be locked when not in use, even if in a garage.

As to the short trips, two things are happening: the battery is being drained and the oil is being weakened. If at all possible, I'd extend driving periods or break things up so you're not taking multiple, short drives in series.

As mentioned above, a tender device would be worthwhile. I'll attach a link that could help orient what can be done. Once installed, it's as simple as plugging in the car.

https://www.mustang6g.com/forums/threads/batter-tender-battery-connection.172738/

Enclosed are some links which will provide conceptual information on keys, security and charging systems.

A primer explaining 6G Active Anti-Theft, Intelligent Access, Passive Anti-Theft and TPMS.

Attached is an updated primer on charging systems.

Edit,

When the new battery was installed, a BMS reset should have been accomplished. The following link will explain how. If installed at a Ford dealer, odds are good they did the reset. If you accomplished yourself, great. If the swap was at a local shop, they might not have done it.

https://www.mustang6g.com/forums/threads/bms-reset-no-tools-required.151602/

The activity is akin to resetting the Oil Life Monitor. It tells the car a new battery is in-place, so the charging system adjusts accordingly.

 

[ORRadtech]

Another thing that hasn't been brought up is that allowing a lead acid battery to significantly discharge can cause sulfate and shorten even a new batteries life. Repeated deep discharges compound the problem. And simply starting and running the car is not a sufficient way to charge a low battery. Car charging systems have never been meant to fully charge a low/weak battery. They are meant to replenish what the starter uses and to operate the car when running.
Also, most people don't realize, a new battery should be given a full charge before its first use. New batteries do come "ready to use" but they seldom have a full charge. Topping off the charge before the first use will give it the best chance at a long life.

 

[Garfy]

Wow! Thank you for this detailed response. I never knew about this. I had a 2003 Mustang GT and always kept my key on the windshield in my garage when parked. But that car has almost no computers lol. So I did the same. I am hoping there is no electrical draws I don’t know of and just my operator stupidity.

I was able to find a BATTERY VOLTAGE on my Mustang and it read 9.5!!! That’s low but I was able to start it every time.

You're fortunate it started. The industry pretty much agreed that 9.6V is the point when most vehicles won't start and on Fords back in the 70's it was 10.0V when their starters were the type without a starter mounted solenoid. I don't use my car regularly either (explains why it has just over 10K miles) so I have a maintainer on it once it's been sitting for a few days.

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