Batteries, F 350, 1999, Super Duty
 

New to the forum, but not new to F series pickups (previously owned 1967 F250, and 1995 F150). Recently purchased 1999 F 350 Super Duty, 7.3 liter diesel, DRW, super cab, with custom flat bed, 216,000 miles.

QUESTION: What is the function of the dual batteries? Are both for starting the monster engine, or is one for starting and the other for accessories, or some other reason for dual batteries? Anything I should know abotu the battery setup?

Diesel batteries
 

Mostly it is required to connect 2 high amp batteries together to crank a diesel engine. One battery can start a diesel engine but with a small reserve.
Diesel engines need lots of amperage. Frank

Welcome to the Truck forums guys
As Frank said. You need that short burst of big cranking amps to turn over that big Powerstroke. and to provide big but before that you need to power the glow plugs.
Once the glow plugs have cycled you still need that cranking power at the same
time providing power to the fuel pump to make that huge fuel pressure demand.

So yes to your question, they are both needed and are working together.

hope you never ever have to jump start it.

That's true.
I killed my Dmax over Xmas holidays.
My truck sat for 3 days and didn't move. I went to start it, it didn't even click. Not even an interior light
It took a Volvo on one battery and a booster pack on the other battery to get it to begin to turn over... It was tuff... cause it was cold too.

Batteries are important..
 

Lead acid batteries create great amounts of energy. A battery that indicates 12 volts with a meter, is 75% discharged. Each cell makes 2.1 volts times 6 cells equals 12.6 volts. In any situation, as voltage declines, the amps go higher as a seesaw. The number one cause of alternator failure is .......
poor battery connections. Number one cause of starter failure..... Low voltage in battery. The best changer rate for a battery is a long slow charge.
If battery condition is unknown, turn on the head lites and operate the starter briefly. If head lites turn to a yellow color, battery has low voltage.
To get a good jump from a running engine, allow the cables to be connected for at least 10-15 minutes. Adding voltage from any source is like filling a container with a liquid. Frank

Helpful info Frank