I just found out that I have 2 extra batteries under my rear passenger seat. I am just wondering what they are for. 24 Tremor, 401a. I have the 2k power.

 

Disconnect them and see what does not work, then you will know.

 

On the Powerboost the under seat battery ensures consistent power to electronics during starting events where there may be heavier draw on underhood battery. I suspect it’s something similar.

 

That's interesting. I wonder if the BCM system wants to keep those at like 70 - 80 percent like the main battery, unless you adjust this with Forscan. Probably would not hurt putting them on a charger once a month as well.

 

As I understand it they are charged at the same time as the under hood battery but isolated during start events to maintain consistent voltage for electronics. I’ve never charged it separately. I just periodically hook my NOCO Genius 10 to the main under hood battery and following charge I can see that the under seat battery is also fully charged (I use OBD2 reader MX+ with OBD Link software to monitor both batteries and other systems).

 

If you have Forscan, it's very cheap to buy a license as well, you can change the target from 80% to 95% or whatever you want. I upgraded my battery to an H9 900 CCA and this mod helps keep it charged properly. I wish I could do the same thing on our new Frontier. I put my 10 amp charger on it yesterday and it took 2.5 - 3 hours to top it off vs 25 min on the F150 with the mod.

 

I’ve never tried to do anything through forscan so I don’t know where it’s set but if I’m driving my SOC will bump from the low 80s up to 90% or more pretty quickly. In fact I’ve seen 95% and if I’m trailering our camper 99% SOC and I’ve not had battery issues. Not sure if throwing the charger on every so often has assisted or not but 3 yrs in now all remains good.

 

Defiantly does not hurt. I changed my SOC to 95% and as I mentioned, it takes 25 min to top off the H9 vs 3+ hours at factory 80%. I also don't do many long trips. I generally charge my batteries to full once every 2 weeks. Maybe it's excessive, but I feel it does help with longevity.

 

Do you know for sure what changing that Forscan parameter actually does? As far as I know, there is no publicly available documentation on it. There is, however, very good reason to suspect that it doesn't do what the conventional wisdom thinks it does, i.e. change the static SOC level at which the BMS maintains the battery. There is good reason to believe that this parameter is used by the BMS, for example, to decide when to run a de-sulfating cycle on the AGM battery. If that is true, it seems possible or likely that monkeying with that parameter may impact the longevity of the battery, but is very unlikely to change the observed SOC..
A few years ago there was a rash of reported battery problems, particularly with the Powerboosts. As far as I know, those in the consumer world who carefully experimented with that parameter, have reported that changing the parameter has NO apparent effect on the battery's SOC. It just doesn't seem to make a difference.
However, there is good reason to believe that Ford did indeed make a substantial change to the vehicle's charging strategy a year or so ago which seems to have greatly reduced the incidence of battery issues being reported on these forums.
Long story short - without having insight into the deep details of the engineering behind the BMS system (Ford engineers are not dummies and would not likely have overlooked something as simple as changing the Forscan parameter), and particularly without clear knowledge as to what the Forscan SOC parameter does, it seems either not useful or possibly damaging to monkey around with it.
YMMV..

 

Those are 2 12v 7.5ah AGMs wired in series to create a 24v transient buffer for the 2nd alternator that runs at 24v for powering the 2kW PPOB inverter your truck comes with.