2025 PowerBoost Drawing Power from Trailer Battery

[P.S.N.]

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



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.



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.



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?).

I'm sorry that happened to your battery. Reading your post makes me glad I am acquiring a battery tender for my PB (I'm learning from yours and others experiences).

It was the PB Facebook group that taught me how I could save gas by not always towing in tow/hall. So not using tow/hall all the time is not "outside of the norm" as you may think.

Sharing what happened to me with my old truck has nothing to do with whatever you said/wrote; that is me being happy that our F150s have a good battery isolator that my old truck did not (no need to be defensive).

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[P.S.N.]

More interesting 2025 F150 PowerBoost seven-way behavior.

As I was moving my trailer around my property today, I decided to record some more power flow numbers between my truck and trailer via my trailer's shunt. My trailer's LFP was pretty full and it looked like my PB was slowly topping it off. Then I put my truck in park and opened the driver's door to check my trailer's position--EcoBoost was idling--I noticed that my truck immediately stopped providing power to my trailer and the flow reversed (see attached video). Once I closed the driver's door, my truck started pushing power to my trailer again. I repeated this three times with the same result and my truck responded immediately with the opening and closing of the driver's door.

This is interesting behavior, at least to me. There is probably a good reason why the F150 does this but I have no idea as to why (failsafe of some sort).

Note that once my trailer's LFP was completely full, the flow from my truck stopped with no reverse flow detected. Although my truck did top off my trailer's LFP at 14.6V, that is very, very full for a lithium. The manufacturer of my LFP recommends a top charge at 14.4V for battery longevity, so I still may disconnect the charge line at my trailer, just to be safe.

 

[Snakebitten]

Nothing to do with the trailer wire specifically, but if you are monitoring your 12V voltage from the DC/DC converter, either by voltmeter or PID, you will see it drop from somewhere as high as 14.7V to 12.7V when you open the driver's door.

I can almost always get 14.7V with the HVAC fan speed on 5, the FOB in the truck, and the driver's door closed.

If I change any of those attributes, like taking the FOB out of the truck, or lowering the fan speed, I don't get the guaranteed 14.7V from the "alternator".

One of the many quirks (Easter eggs?) of the mighty Powerboost.

 

[tsigwing]

Hooked up my trailer for a trip, took these pictures of both my solar, trailer battery and PB battery. I have a victron bluetooth monitor on my trailer and a bluetooth monitor on my truck. I did not take a picture when the truck was running. Both voltages where at ~14v. On the trailer side, that could be because it is early morning with shadows on the solar. Or it could be that with the truck running, the voltages equal out. Certainly when I turned off the truck, the voltages are different.

I'll try to get another reading when underway to see what is happening.

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