I noticed that the passenger side battery cable is starting to crack a little where it forms into the terminal. I have a new Motorcraft cable set on the way.

In the meantime, I'm curious to know if the passenger battery is being utilized fully. I unhooked the drivers side battery to replace the filter and discovered that the truck wouldn't turn over - no lights, nothing.

As soon as I connected the drivers side battery back again, it started normally. Is that how the F250 7.3 truck batteries are supposed to work?

 

No, the batteries are wired in parallel (still a 12v system) and as such your truck should light up and turn over, it may be a little sluggish especially if the GP's are lit, but it should at least try. You may want to check your connections on that battery and/or have it tested.

 

Agreed. The truck in my sig will start and light with only one battery connected, and it does not matter which one.

Parallel-positive to positive, negagtive to negative- voltage remains the same, amps double if all batteries are equally healthy.

 

Thanks that confirms what I needed to know.. The passenger battery terminal isn't carry much if any current due to a crack. I have new terminals on the way.

 

That's my redneck way of load checking my batteries. Disconnect one, start truck, reconnect that one and disconnect other, start truck. Weak ones show up pretty obviously with this method especially if the glowplugs are cycling.

 

The Engine (Electric Starter) requires 400 AMPS to Turn the Engine Over.


FYI: Parallel increase Amperage Hours (Ah)/ Series increases Voltage (V).


So, with two 750CCA FWC Batteries in "Parallel" you obtain 1,500 CCA (available at32*F - reduced as temperature rises above 80*F, Flooded WCB hate heat! It’s like their Kryptonite).

Why so much needed? Minimal Operational Requirements


The Glow Plugs require 80 - 120 AMPS up to 120 Sec of operation.


The Vehicle itself uses about 100 AMPS +/- depending upon accessories, options, and so on. Compression, Compression, Compression uses it up rapidly!

FWC Batteries need to maintain 50% of the Ah under 100% load. Drawing such anamount of Amperage is very hard on a FWC Storage System. That's why when your batteries are a few years old you may have to recharge them after a no start with just a few minutes of cranking or when they sit for a week. The "Ah" is dying. Anything below 70% Ah is worthless.

A FWC Battery must maintain 50% + of its amperage during its biggest calculated draw in order to be able to regain and maintain its charge.


If you’re starting your vehicle on one battery, you’re literally “killing” its ability to regain and maintain its capacity until exhausted (70% Ah).

Here is the Math:

1,500 Ah (1,280Operational)
-400 (Starter)
-400 (Reserve)
-120 (GPO peration)
-100 (Vehicle Operation – Fuel Pump, Vacuum Pump, Illumination, PCM, IDM, etc.)

480 AMPS (Ah) Remain (50%-60% of its total rating - 384 Ah Operational) until the Alternator successfully replaces what was used.

Here is a bit of information many people aren’t aware of. The Starter is basically a 12v Generator in that there is an electrical field which causes rotation. Energy is a by-product of its operation.


But, did you know it also generates a great amount of both Voltage and Amperage when it turns? This accounts for more than 50% of the heat that is generated (no pun). So, if you’re Starter and Batteries are operating as designed, the Starter itself is creating up to 200 AMPS and you require 400 AMPS. The “Net” Amperage you’re using from your Batteries is only 200 AMPS.

This has a lot to do with why our Batteries last or, don’t last. The amount of time you spend changing out batteries is directly related to the health of the system in its entirety. Not just one part i.e.: Batteries


Ever wonder why a new car battery seems to last for six, seven, eight years? Because everything is new and operating at its peak performance.


Put a used Starter, Alternator, and Belt on a new car and the Battery will only last a couple years.

 

Good write-up! Thanks for the info.

 

on my 02, if the driver side battery is disconnected it will still start. but if the wires going into the computer are disconnected from the cable connection at the driver side battery, it will not start. from what i can figure, the computer takes it's power from the driver side battery connections.