I have a 2010 F250 PSD with two batteries and two alternators. Does the electrical power come off both batteries equally or does one battery start the truck and the other run the truck? If I leave the lights on would one battery be dead or both batteries? If one battery needs replacing should I replace both at the same time? Thanks for the help

 

Both batteries start the truck. If you leave the lights on both batteries will be dead. If u have one bad battery always replace them both. As if u only replace one the other one may be weak and it will discharge the new one. On my semi trucks when the batteries show signs of getting weak I always replace all four and it may only really have one that has a short in the plates but it is just simpler to replace them all and way less trouble in the future. A set of batteries will generally last 4 to 6 years if u are lucky.

 

My son drives with 12 years old battery.
You need to check the manual how the system works. What is the second alternator for? That would indicate 2 independent power systems in the truck. Than PSD takes 2 batteries to start. Are you sure you don't have 3rd battery?

 

The second alternator provides more power to the 2 batteries and redundancy if one fails. There is not battery isolator from the factory so both batteries are charged and discharged at the same time,

 

Thats very old for a set of batteries. Hope he's good at walking as he very well have to at any time. I think 7 years is the most i ever got out of a battery in a 1971 chevy nova puchased new. The first battery or set in a vehicle will almost always outlast any future set as when everything is new it just seems to be easyier on the batteries. 12 years, most mariages don't last that long.

 

The batteries in my truck lasted 10 years. I just replaced them last winter. Batteries can last a long time if they remain at good state of charge, don't get too hot, and aren't subjected to excessive vibration. The batteries in my Olds Aurora are placed under the rear seats in the interior. 12 years old and still fine.

You have 2 batteries in your truck to meet power needed for cold weather starting. You have two alternators because you have optional electrical systems that require high power. A large single alternator could have been used, but it was probably cheaper for Ford to install a second alternator on top of the standard alternator.

 

Thanks for the answers. One of the reasons that I ask this question was that in my 1997 Chevy 2500 that I replaced with the Ford the battery would last 2 years and that was it. I could buy the most expensive battery or the cheapest and it would last only 2 years. I had alternators and regulators replaced and it was still 2 years. So when it got close to 2 years I would replace the battery so I would not have to walk.
Hopefully with this 2 battery system that Ford installed I will still have 1 good battery to start the truck. Thanks

 

The key to automotive batteries and making them last is to never allow them to fully discharge. A battery can only withstand on average 10 discharges before it is junk.

This is why they make special deep cycle batteries for trolling motors and RV use, Those can withstand the discharge cycle, but generally you can't draw as many amps from them like an automotive battery.