How Many Volts do our trucks really need?

[Old Hat]

A year ago I installed a cigarette lighter voltage meter into my '22 XLT to monitor the original battery. Every morning when I switched the key to on, (not start) it would usually read 12.2 or 12.1, whether it sat overnight or for several days. My multi meter at the battery terminals confirmed the reading.

I never had any battery issues or notifications the entire time I've owned the truck. Convinced by this forum that original Ford batteries were deficient and higher voltage was required, I installed a new battery two months ago only to find that it ended up performing the same. Apparently, at least in my case, that’s just where the BMS wants the voltage to be.

For comparison I plugged the same meter into our 2015 Mercedes for a few days (with a two year old AGM battery) where I also found 12.2 or 12.1 volts at first key on. This car ran the original battery for 7 or 8 years and I only replaced it because I felt that was long enough, I didn’t want to risk failure by running it longer. Just like the truck, it also never any battery issues. So why the concern for higher voltage? It seems these batteries work fine in the lower 12’s, and last plenty long there too.

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[Kanuck]

This is my take on the electrical and battery system on my truck works....

These trucks work on 12 volts. It is not the voltage but the current required. Volts X Current (Amps) = Power (Watts). With all the modules on the truck, each drawing power from the battery, the load on the battery is a lot more than what your 2015 Benze needs. I was working on my truck one day and had it running. After I shut it off, I connected my meters. The battery was showing 12.8 volts but had a current draw of 3.8 amps with the truck turned off. This reading slowed drop down approx .02 amps after about 5 minutes. during the 5 minutes, power was being taken out of the battery until the modules shut down. On these trucks, some modules either don't shut down, approach sensors, security system or TCU listening for a call from Ford. The OEM battery just didn't seem to like the way they were being used in these trucks.

 

[Snakebitten]

The issue with using the cigarette lighter voltmeter is that it's difficult to get a voltage reading without waking the truck up first.
Those 12.1 & 12.2 volt readings while you are in accessory mode, in my opinion, are indicative of a fairly healthy battery. And if I had to guess, the resting voltage of that battery before you woke the truck up was likely 12.5V or better.

 

[Old Hat]

The issue with using the cigarette lighter voltmeter is that it's difficult to get a voltage reading without waking the truck up first.
Those 12.1 & 12.2 volt readings while you are in accessory mode, in my opinion, are indicative of a fairly healthy battery. And if I had to guess, the resting voltage of that battery before you woke the truck up was likely 12.5V or better.

I kinda suspected that. Even opening the hood to check the battery directly wakes it. When I took it out the original battery tested at 12.4 on the bench... and held there for 2 months untouched before slowly dropping. Since it's good I decided to keep it instead of returning it for the $20 core so now I have a spare on hand.

This is my take on the electrical and battery system on my truck works....

These trucks work on 12 volts. It is not the voltage but the current required. Volts X Current (Amps) = Power (Watts). With all the modules on the truck, each drawing power from the battery, the load on the battery is a lot more than what your 2015 Benze needs. I was working on my truck one day and had it running. After I shut it off, I connected my meters. The battery was showing 12.8 volts but had a current draw of 3.8 amps with the truck turned off. This reading slowed drop down approx .02 amps after about 5 minutes. during the 5 minutes, power was being taken out of the battery until the modules shut down. On these trucks, some modules either don't shut down, approach sensors, security system or TCU listening for a call from Ford. The OEM battery just didn't seem to like the way they were being used in these trucks.

This makes sense. Yet monitoring voltage and posting readings seems popular around here. As is bumping up SOC, using tenders and other stuff to raise it. So just what is the magic number? I thought I also read something from Ford stating that the BMS charging strategy is limited to help the battery last longer.

 

[Snakebitten]

I've posted it many times, so some around here will give the eye roll.... ??

But with these modern vehicles that never really sleep, and so it's difficult to know what's going on with the battery while you are in the house or office, you need a method to check/monitor the "Resting voltage".

I have installed a small inexpensive Bluetooth voltmeter in my 2022 Powerboost and 2023 Mach-E. (Both vehicles are notorious for surprising the owner with a low voltage issues)

It mounts directly to the +- posts of the AGM

And don't worry, it has an almost imperceivable draw itself.

It allows you to get a voltage reading without disturbing the vehicle. You don't even have to approach it.

This is real time, and I simply opened the app on my smartphone. The Mach-E is parked just outside the RV I'm sitting in.

Don't let the voltage reading mislead you. That tiny little H3 AGM isn't resting at 13.54V. Rather the car is currently plugged into the L2 EVSE charger, and so while I'm charging the High Voltage battery, the dc/DC converter is charging the AGM.

The bonus to the Bluetooth voltometer is that it is storing the voltage reading every few seconds, and the app downloads that logging. This allows you to witness what the battery voltage is 24/7/365

THAT is what would have likely led you NOT to purchase a new battery, because you would have verified your resting voltage as 12.3V or more.

Here is the log for the Mach-E today

Wherever you place your finger, you get the red vertical line with the exact timestamp and voltage for that moment. You can see that the car was resting at 12.84V sitting in the parking spot at the office today.

Bluetooth voltometer is about $25

 

[Gros Ventre]

A typical starter needs at least 10.5VDC with many amps to start the engine. If you opened the door or even walked close enough (~30 feet) to detect the key fob, the truck alerted and started some of its modules. These lower battery voltage by current draw. What you need to be doing is when you get home, unlatch the hood, then leave the key fob far, far away. Come out at least 1 1/2 to 2 hours later (or the next morning) and measure the battery voltage with a voltmeter on the terminals. Any load on the battery lowers voltage, that's just a normal thing because there's internal resistance and voltage drop equals resistance times current. During the start event you'd see voltage drop several volts because the current is several hundred amps. Remember, as soon as you trigger one or more modules, you're not seeing true battery no-load voltage. That no-load voltage is what will tell you something about battery health. The second thing that tells you battery health is what voltage does it drop to during engine cranking before it fires. The lower that cranking voltage the poorer the health of your battery. I installed a dashboard voltmeter. One way to get a snapshot of battery health is to turn the truck on without starting the engine. I observe around 12.4-12.6VDC. That's reasonably good after three years usage.

 

[Old Hat]

The only reason I didn't get the bluetooth voltage reader is because I don't have a smart phone. The dash / cig lighter meter is not taking true resting voltage but the readings you get at all other times are very consistent. If you monitor it regularly you'll know if the battery is getting weak or something else is not working right.

 

[Gros Ventre]

The only reason I didn't get the bluetooth voltage reader is because I don't have a smart phone. The dash / cig lighter meter is not taking true resting voltage but the readings you get at all other times are very consistent. If you monitor it regularly you'll know if the battery is getting weak or something else is not working right.

If it can be tilted so you can see it thru a window, then if you approach the truck without a key fob, you'll get a true resting voltage. It does need to be in an outlet that is energized key-off, engine-off.

 

[Old Hat]

If it can be tilted so you can see it thru a window, then if you approach the truck without a key fob, you'll get a true resting voltage. It does need to be in an outlet that is energized key-off, engine-off.

Right. What I'm saying is a true resting voltage reading is not necessary. When accessory voltage is consistently 12.1 or 12.2 all is good. This is what I found on mine with both the original battery and a new one, even after sitting unused for days. Reading the threads here lead me to believe I needed more but I never had a problem so I'm done worrying about it.

 

[Snakebitten]

Less about worry, and more about understanding and knowing how things work on this crazy electrified truck.

And your personal experience hasn't been nearly as problematic as some others. Lots of fellas had the issues that come with lower voltage than 12.1 Volts.

 

[Gros Ventre]

Right. What I'm saying is a true resting voltage reading is not necessary. When accessory voltage is consistently 12.1 or 12.2 all is good. This is what I found on mine with both the original battery and a new one, even after sitting unused for days. Reading the threads here lead me to believe I needed more but I never had a problem so I'm done worrying about it.

So long as the modules that come on are the same, you are correct, the drain will be the same and you can then infer battery health. However, make sure of that. Also, the real battery health come when under a heavy load. A battery that has developed sulfation can present good voltages at low load yet fail at a high load because the plate surface area is reduced.

 

[Old Hat]

Less about worry, and more about understanding and knowing how things work on this crazy electrified truck.

And your personal experience hasn't been nearly as problematic as some others. Lots of fellas had the issues that come with lower voltage than 12.1 Volts.

As you pointed out earlier (and I was starting to suspect) 12.1 volts when awake and in accessory mode is likely equivalent to higher voltage in full resting mode. And now I proved that this is in fact the case.

Yesterday I parked the truck at 4pm and left the hood open. At 5:30 I took my first reading directly from the battery terminals, and then a few more times prior to start up this morning.

1/19/25
5:30pm, 12.52v
11:00pm, 12.52v

1/20/25
7:30am, 12.51v
9:45am, 12.52v

9:45am, open door, wake truck, turn on accessory: 12.2 at the cig lighter meter and battery terminals.

The 12.1 and 12.2 I see every morning prior to start up is equal to 12.4-12.5 resting on a bluetooth reader, and in my opinion is plenty and normal.

 

[Snakebitten]

That's really good data collection and data points.

And it pretty much represents my reasoning to intervene with "external charging" anytime I found the resting voltage drop below 12.3V

I'm not saying that should be anyone else's threshold, but it was mine, and I believe it's the reason I still have a functional oem underhood Motorcraft AGM at nearly 3 years old.
It was spared the multiple opportunities to be weakened/damaged by spending time at very low SOC.

Thanks for the post.

 

[powerboatr]

I've posted it many times, so some around here will give the eye roll.... ??

But with these modern vehicles that never really sleep, and so it's difficult to know what's going on with the battery while you are in the house or office, you need a method to check/monitor the "Resting voltage".

I have installed a small inexpensive Bluetooth voltmeter in my 2022 Powerboost and 2023 Mach-E. (Both vehicles are notorious for surprising the owner with a low voltage issues)

It mounts directly to the +- posts of the AGM

And don't worry, it has an almost imperceivable draw itself.

It allows you to get a voltage reading without disturbing the vehicle. You don't even have to approach it.

This is real time, and I simply opened the app on my smartphone. The Mach-E is parked just outside the RV I'm sitting in.

Don't let the voltage reading mislead you. That tiny little H3 AGM isn't resting at 13.54V. Rather the car is currently plugged into the L2 EVSE charger, and so while I'm charging the High Voltage battery, the dc/DC converter is charging the AGM.

The bonus to the Bluetooth voltometer is that it is storing the voltage reading every few seconds, and the app downloads that logging. This allows you to witness what the battery voltage is 24/7/365

THAT is what would have likely led you NOT to purchase a new battery, because you would have verified your resting voltage as 12.3V or more.

Here is the log for the Mach-E today

Wherever you place your finger, you get the red vertical line with the exact timestamp and voltage for that moment. You can see that the car was resting at 12.84V sitting in the parking spot at the office today.

Bluetooth voltometer is about $25

Cool little item
thanks

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