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From: Ted Heise <theise@panix.com>
Newsgroups: rec.outdoors.rv-travel
Subject: Re: battery change questions
Date: Sun, 4 Aug 2024 20:10:57 -0000 (UTC)
Organization: My own, such as it is
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On Sat, 3 Aug 2024 15:38:30 -0500,
  George Anthony <ganthony@gmail.org> wrote:
>  On 8/3/2024 1:00 PM, bfh wrote:
> > Ted Heise wrote:
> >> On Fri, 2 Aug 2024 23:13:42 -0400,
> >>    bfh <redydog@rye.net> wrote:
> >>>   Ted Heise wrote:

> >>>> But how did you charge the trailer battery?
> >>>
> >>>   It charged through the 7-pin when driving, and with the
> >>>   built-in charger when we had shore power. I don't remember
> >>>   having any battery problems when flatspotting, but we rarely
> >>>   stayed in one place longer than 2 days/nights. Plus, we weren't
> >>>   spoiled back then, and all we used when parked were 1 - maybe 2
> >>>   - lights and the water pump.
> >>
> >> Okay, charging from the 7-pin is what I'd expect, but I 
> >> haven't seen any evidence of that happening since I put in 
> >> the new LiFEPO4 battery.  Admittedly, it's just been one trip 
> >> of ~5 days.
> >>
> >> I do wonder if the battery has to reach some lower SOC than 
> >> I've seen (85%?) for charging from the 7-pin to kick in.  
> >> Operation of the Dometic battery monitor is still largely a 
> >> mystery to me...
> >>
> >> https://www.amazon.com/Go-Power-GP-BMK-25-Battery-Monitor/dp/B09NRXD9G8
> >>
> >> Is it possible the 7-pin will actually charge the battery if 
> >> it gets to a lower SOC?  If yes, do the GP-BMK-25 settings 
> >> make a difference in this level?  I can't tell from the 
> >> "manual" and mre broadly havn't been able to get a good 
> >> unserstanding of how it works.
> 
>  I really don't think it will charge from the 7-pin connection 
>  if the battery is low. At least not with the standard size wire 
>  you now have. By the way, I may have missed it but did you ever 
>  verify if you have voltage coming through the 7-pin connection 
>  at the positive battery cable on the trailer battery?

Yes, I've checked the 1 and 4 pins on the 7-pin receptacle with a 
multimeter, and there is 12 V there--even when the car is shut 
off.  I'm also able to run 12 V equipment (e.g., tongue jack, 
lights, exhaust fans) when the trailer (without any battery) is 
connected to the 7-pin on the tow vehicle.

The thing that doesn't make sense to me is that when the battery 
and 7-pin are both connected, the battery still reports it's 
discharging.  I could get that it doesn't charge much, but to be 
discharging just seems unexpected--like something in the trailer 
(e.g., the PD4000 power control enter) is not supplying anything 
to the battery.  FWIW, it does charge when the trailer is hooked 
to shore power.

-- 
Ted Heise      <theise@panix.com>       West Lafayette, IN, USA