Hi folks,
First time poster here.

I have a 2021 F350 Lariat 7.3 gas, SRW. It is equipped the dual batteries and a 397A alternator.

Can someone explain how the dual batteries are connected? It would seem logical that they would be isolated such that accessories are powered by one battery and the other battery is used for starting and operating the engine. That way, if you leave some accessory on and it drains the (accessory) battery, at least you'll be able to restart the engine and recharge the accessory battery. On the other hand, I can understand that they might be simply connect in parallel so that you'll get the max available capacity to power hungry accessories? Any info?

Thanks
Ken

 

The batteries are in parallel so if one draws down the other draws down. If you replace one you are supposed to replace both because having 1 good and 1 bad battery will kill your 1 good battery prematurely.

 

Yup, both batteries are used, neither is isolated from the other.

 

Actually from a wiring standpoint it would NOT make sense to have the battery isolated, as that would complicate charging them via the alternator.

As said above, they are connected in parallel, to keep the system 12VDC while increasing the available amperage. This is beneficial for trucks that will see more frequent high-amp-draw situations, such as running a snow plow or winch. It can also be beneficial for those who tow a lot (counteracts weak RV batteries), or who have to start/stop their truck a lot (delivery drivers).

 

 

So that means to charge batteries or use a battery tender, you only have to connect t to one battery to take care of both.

 

Just think of the two batteries as functionally one very large battery.

 

The OP and I had the same misconception, sort of, where it has been stated on gas trucks the two batteries are not always connected in parallel as in the case of the diesels. It has been stated, incorrectly, that when the truck is shut off a relay opens between the batteries, allowing one to be used for accessories and the other held in reserve for engine start. The purpose of this scheme is to always have a fresh, fully charged battery for engine start.

While I think this would be a dandy idea, alas and woe, it is not the case.

Thanks for the good information.

 

OP, there are also 2 alternators to make 397a.