Is the auto start stop battery always connected ?

[Muffin Top]

Whenever I'm at home, not driving El Bronco, its main battery is plugged into a Schumaker charger that's seemed to perform well. For my other vehicles, their AGM batteries will read 12.8V or higher after a short drive for errands, because they're all plugged in when parked, like El Bronco.

However, El Bronco's voltage reads low after a short drive, so I wonder if that means the auto start stop battery is only charged when the vehicle is being driven?

After sitting for a few days, the auto start stop battery is low? So after a short drive the main battery looks low, even though it was topped off while parked?

Hoping someone who's into electronics knows whether the auto start stop battery is always connected, or whether it's only charged when the vehicle is driven.

By the way, I never use auto start stop. Start-up routine includes promptly de-activating. It's hot in TX, so it doesn't make sense to turn off the a/c compressor. And I wouldn't want to stress that auto start stop battery when it appears that I have a compromised battery.

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[Ducati1098]

I don’t follow.
I’m confused by what you mean as far as the “auto start stop battery” and the “main battery”
There’s only 1 battery

 

[brkdncr]

The ecu doesn’t charge the battery to 100%. This helps the battery last longer.

 

[Brian_B]

12.5V is “normal” resting (engine off no draw) voltage for the AGM batteries and default charging strategy, which equates to 80% State of Charge

The battery will typically only charge if resting voltage is less than that, temporarily to make up for large drains (like starting the engine), or it will opportunistically charge over that if you are engine breaking (like cruising down hill)

Because of this charging strategy (largely a fuel conservation effort), short trips can have the effect of not being able to recharge the battery fully, and State of Charge slowly lowering over time with lots of short trips. Usually just a trickle charger overnight to top it back off fixes it right up.

the battery is always connected, but the vehicle can do a fairly primitive form of load shedding if voltage drops too low while it is off, or it has been a while since the last start (10-14 days) - commonly referred to as Deep Sleep, it will disable the telematics (OTA updates), courtesy lamps, and other power draws while the vehicle is off to try to preserve enough power to start

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So, after saying all that - to the OP, who keeps their vehicle on a charger most of the time - the reason they aren’t seeing much more than 12.8 V while running is because the Bronco knows it has a fully charged battery, and is saving fuel by not overcharging it. If you were to coast downhill for an appreciable length of time, I bet you would see the charger tick up to 13.8 or higher as it takes advantage of engine braking, but otherwise will just make enough power with the alternator to “float” the battery and let it idle.

With the engine running the alternator is controlled by the computer and voltages anywhere from mid-12 to low-15 are perfectly normal to see.

 

[adam1991]

I don’t follow.
I’m confused by what you mean as far as the “auto start stop battery” and the “main battery”
There’s only 1 battery

sounds like he comes from Stellantis, where they do use a separate (smaller) battery.

 

[Ducati1098]

sounds like he comes from Stellantis, where they do use a separate (smaller) battery.

Interesting. Had no idea they did that.

 

[adam1991]

Interesting. Had no idea they did that.

https://www.jlwranglerforums.com/fo...ery-where-is-it-and-whats-its-function.76335/

 

[Roger123]

Interesting. Had no idea they did that.

It's all in the name of lowering emissions by adding an entirely separate battery system to manage the Auto Stop/ Start. Saving the planet one extra battery at a time.

 

[Beggsie]

I don’t follow.
I’m confused by what you mean as far as the “auto start stop battery” and the “main battery”
There’s only 1 battery

Jeeps have the little secondary battery for the auto stop-start, Broncos do not as far as I know.

 

[Ducati1098]

It's all in the name of lowering emissions by adding an entirely separate battery system to manage the Auto Stop/ Start. Saving the planet one extra battery at a time.

Ahh yes, that totally makes sense now

 

[CarGuy]

sounds like he comes from Stellantis, where they do use a separate (smaller) battery.

Mercedes as well.

 

[Bschurr]

Mercedes as well.

And Land Rover and many others

 

[Brian_B]

A second battery for the electronics makes perfect sense. One for the starter not so much. There is so much other rather large electric loads other than the starter - electric steering, electric braking, electric fans, etc… but the electronic computers are the most sensitive to voltage fluctuations.

 

[retiredarmymp]

I follow “Jeep Gladiator Problems” page on Facebook because every once in awhile I get an itch to get a gladiator. Reading their post always confirms how much I love my Bronco and won’t get a gladiator, but one of the biggest complaints is the small auxiliary battery because it can cause a complete loss of power in the vehicle,and most jeepers override and eliminate it.

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