2025 PowerBoost Drawing Power from Trailer Battery

[P.S.N.]

I just ran the test for a sixth time this morning with very different results.

Before I got started, I let my PB idle to charge the high voltage battery until it turned itself off, just like I did in my other tests.

Like before, I turned everything off that I could and recorded a 2W draw from some small LED lights, CO2 detector, etc. as you can see at the beginning of the attached video. Around eight seconds in, I turn my PB on, not start just on. For the first four seconds of being on, my PB was pulling power from my trailer. After six seconds of being in accessory mode, my truck starts providing a charge to my trailer (now that's what I want to see). Twenty-six seconds into the video, I turn my PB fully on and capture an interesting surge of power from my truck to the trailer's battery (about 160W), then it quickly saddles down and continues to provide a charge to my trailer until I turn my PB off.

So I am no longer worried about draining my LPF in my trailer. However, I would love to understand why my first five tests showed only a draw of power from trailer to truck while this morning's test showed a combination of both but mostly a charge from truck to trailer.

Is that 160W surge from truck to trailer battery at full startup something I need to worry about; can that damage anything on the trailer side of things?

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[Davexxxx]

I just ran the test for a sixth time this morning with very different results.

Before I got started, I let my PB idle to charge the high voltage battery until it turned itself off, just like I did in my other tests.

Like before, I turned everything off that I could and recorded a 2W draw from some small LED lights, CO2 detector, etc. as you can see at the beginning of the attached video. Around eight seconds in, I turn my PB on, not start just on. For the first four seconds of being on, my PB was pulling power from my trailer. After six seconds of being in start mode, my truck starts providing a charge to the trailer (now that's what I want to see). Twenty-six seconds into the video, I turn my PB fully on and capture an interesting surge of power from my truck to the trailer's battery (about 160W), then it quickly saddles down and continues to provide a charge to my trailer's battery until I turn my PB off at the end of the video.

So I am no longer worried about draining my LPF in my trailer. However, I would love to understand why my first five tests showed only a draw of power from trailer to truck while this mornings test showed a combination of both but mostly a charge from truck to trailer.

Is that 160W surge from truck to trailer battery at full start something I need to worry about; can that damage anything on the trailer side of things?

I think you made all of this overly complicated and that provided strange results.

In actual use, when hooked to the trailer, you'll be in tow haul, which unless in park, doesn't turn off the ICE. Measuring when in electric mode is irrelevant, because you'll almost never be in that mode, with the trailer hooked up.

Its common practice to unhook, once parked for the day.

 

[JEB]

I just ran the test for a sixth time this morning with very different results.

Before I got started, I let my PB idle to charge the high voltage battery until it turned itself off, just like I did in my other tests.

Like before, I turned everything off that I could and recorded a 2W draw from some small LED lights, CO2 detector, etc. as you can see at the beginning of the attached video. Around eight seconds in, I turn my PB on, not start just on. For the first four seconds of being on, my PB was pulling power from my trailer. After six seconds of being in start mode, my truck starts providing a charge to the trailer (now that's what I want to see). Twenty-six seconds into the video, I turn my PB fully on and capture an interesting surge of power from my truck to the trailer's battery (about 160W), then it quickly saddles down and continues to provide a charge to my trailer's battery until I turn my PB off at the end of the video.

So I am no longer worried about draining my LPF in my trailer. However, I would love to understand why my first five tests showed only a draw of power from trailer to truck while this mornings test showed a combination of both but mostly a charge from truck to trailer.

Is that 160W surge from truck to trailer battery at full start something I need to worry about; can that damage anything on the trailer side of things?

Makes sense to me. When you turned on the truck in accessory only mode, system voltage initially dropped because it wasn’t getting a charge from the charging system. This created an imbalance with the truck voltage dropping below the house battery voltage. Then the hybrid system stepped in to restore system voltage and provide a charge to the trailer. Then when you started the truck, you got an initial surge of power from the charging system when the engine cranked, which settled down quickly since the truck battery wasn’t discharged.

I must admit I am surprised that the trailer could provide a material or measurable charge to the truck given the architecture (distance, wire gauge, “smart” connector interference) but you appear to have confirmed it. I stand corrected.

 

[P.S.N.]

I think you made all of this overly complicated and that provided strange results.

In actual use, when hooked to the trailer, you'll be in tow haul, which unless in park, doesn't turn off the ICE. Measuring when in electric mode is irrelevant, because you'll almost never be in that mode, with the trailer hooked up.

Its common practice to unhook, once parked for the day.

I only use tow/hall when towing in the hills for I like being able to tow in electric mode when possible, of course when costing or maintaining a slow speed.

Regardless, one of my initial tests was conducted driving down the highway at 55 MPH in normal mode. Yes, this morning's test (test #6) was done in my driveway, but the ICE was idling when I turned my PB fully on, just like it was during the other tests when I recorded a draw from trailer to truck. Test #6 was the only time I recorded a plus of power going to my trailer. Hopefully I can repeat that positive result later whenever I do test #7.

 

[Davexxxx]

Do as you wish but I don't know why you would even think to measure such a thing while in accessory mode. You certainly wouldn't be checking the charging system at that point. My truck is either on, or off and if hooked to the trailer via the 7 pin, in tow haul.

 

[P.S.N.]

Do as you wish but I don't know why you would even think to measure such a thing while in accessory mode. You certainly wouldn't be checking the charging system at that point. My truck is either on, or off and if hooked to the trailer via the 7 pin, in tow haul.

Bash me all you want. I had the opportunity to record behavior in "accessory mode" so I did just to see what happens, not to tell you and others that is how one uses a truck and trailer ("accessory mode" was a learning opportunity only).

I love the performance of towing in tow/hall for it really is tuned just right for that type of work. But it does decrease my towing MPG. If I keep it in normal or eco modes on flat terrain, I can see a 2 MPG increase when towing, which is nice.

 

[Davexxxx]

Not bashing but since you were doing things outside of the norm and that wasn't clear to me until your last couple posts, it made it more difficult to help.

 

[Snakebitten]

Tow haul vs normal mode are no different when driving down the road, regarding the truck's 12V charging.

The DC/DC converter is providing 12V current sourced from the HV battery regardless of whether ICE is on/off.

And although I don't have a Powerboost sans the BISG, I do not believe that Ford altered the DC/DC converter's role in any way between the two builds. The BISG removal only required Ford to alter the ICE starting logic to accommodate removing 1 of several methods to turn the crankshaft over for an ignition event.

I really don't believe the 12V bus was altered in any way other than the removal of the high amperage 12V battery cable used to supply 12V to a belt driven method of turning the crankshaft.

 

[Gros Ventre]

The higher voltage battery will charge into the lower voltage battery bank. Thus the LiFPO14 battery will discharge into the truck batteries. The Lead-acid batteries will accept the charge while over-charging the truck batteries as a result. How far will they overcharge? Dono!!!! Long term the Overcharging will damage lead-acid a battery (They can literally boil off the battery acid). That is part of the issue in Ford setting the 12VDC battery system voltage leaving the truck battery charged to 80%.

 

[P.S.N.]

All,

Check my logic on this, please.

I think most of my initial power draw tests captured moments when my PowerBoost was not in its 12V charge cycle until my recent test when I saw a small but positive charge coming from my F150 to my trailer's LFP battery. Reviewing it all, would you agree or disagree and why that the power flow to/from a trailer equipped with an LFP and the F150 PowerBoost is almost uncontrolled? I say "almost" because there is a battery isolator that prevents power from flowing when the F150 is off and the PowerBoost's BMS will prevent the 12V system from overcharging (or so I have read).

If you agree, then "The RV Tech" (see link), and other RV repair technicians, are correct and even modern trucks, such as the 2025 PowerBoost, are not configured to handle the differences between AGM and LFP systems when connected together via the seven-way (reference: https://www.facebook.com/share/r/16VtaFBfAR/).

 

[Davexxxx]

If you'd get a multi meter with an amp clamp and set up test leads as I described, you'd know for sure for yourself. It really is that easy and ~9K towing miles, confirm no harm to my truck.

It is pretty universal, that units with on board alternators (motor homes, boats) need an LFP capable BIM to protect the alternator. It is equally universal that trucks don't, because of the fusing, wire ga. and length.

But as you use yours outside of the norm, ya pays your money and ya takes your chances.

 

[Davexxxx]

BTW, thinking that the big battery and the 2 AGMs and the charging systems for each, are linked in an unregulated parallel connection can't be right, since the big batt is high voltage.

 

[Davexxxx]

Also, check the fuse panel schematics for your truck. On mine, there is a 30A and a 10A fuse involving trailer connections.

 

[P.S.N.]

If you'd get a multi meter with an amp clamp and set up test leads as I described, you'd know for sure for yourself. It really is that easy and ~9K towing miles, confirm no harm to my truck.

It is pretty universal, that units with on board alternators (motor homes, boats) need an LFP capable BIM to protect the alternator. It is equally universal that trucks don't, because of the fusing, wire ga. and length.

But as you use yours outside of the norm, ya pays your money and ya takes your chances.

Are you still using your original 12V batteries in your PB?

It has become very common for new and some old travel trailers to be outfitted with LFP batteries, so towing one with a PB is not "outside of the norm" anymore, in my opinion. How best to protect things and/or take advantage of this is the goal without wasting a lot of money. It seams to me, and it reads like you believe it too, that there is no harm being done (that's great).

In my old truck, the charge wire was always hot when connected to a trailer, so my LFP equipped trailer would drain my truck battery. It is great that I do not have to worry about that with my PB.

Also, check the fuse panel schematics for your truck. On mine, there is a 30A and a 10A fuse involving trailer connections.

The fusing is interesting. My 2025 PB has seven different blade fuses related to the trailer, three 30A, one 20A, one 15A, one 10A, and one 5A. The manual does not specifically callout the charge wire fuse, which on my old trucks was always it own dedicated fuse.

 

[Davexxxx]

Are you still using your original 12V batteries in your PB?

Body shop replaced the engine batt, when it sat outside for a month in winter and wouldn't take a charge.

It has become very common for new and some old travel trailers to be outfitted with LFP batteries, so towing one with a PB is not "outside of the norm" anymore, in my opinion.

Not using tow haul, is outside of the norm and manufacturers recs. and PB specifically, affects when and whether it goes into electric only mode.

How best to protect things and/or take advantage of this is the goal without wasting a lot of money. It seams to me, and it reads like you believe it too, that there is no harm being done (that's great).

Based on my testing and experience, there is no harm to my truck. YMMV

Some have disconnected the charge wiring on the trailer side of the 7 pin. Some did that, + ran an umbilical, to use PPOB while towing, some like me, have done nothing special and I've yet to see anyone on this website show harm from doing so.

In my old truck, the charge wire was always hot when connected to a trailer, so my LFP equipped trailer would drain my truck battery. It is great that I do not have to worry about that with my PB.

I didn't say that. When parked for the day, I unplug the 7 pin but I've no data to support it, just old habits (best practices?).

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