2005 F-250 FX4 - 6.0 Bullet proofed

If I park my truck with the nose pointing up hill, it seems to start without much, if any, issues at all.

If I park my truck with the nose pointing down hill, the truck acts like it doesn't want to start. It will turn over and sound like the battery is giving out.

Yesterday, my daughter parked the truck with the nose pointing down hill. Truck would not start at all - got to where it wouldn't even turn over - just click like a dead battery.

Ended up having to roll the truck on to a flat surface and hook my wife's Tahoe up with jumper cables. After about 20 minutes of revving the Tahoe up, I was able to get the truck to start. I was connected to the battery on the driver side - assuming this is the "start" battery.

Had the alternator checked and it tested out perfectly fine. I was able to start the truck this morning without any issues - so the battery IS charging.

Could this be a battery that is low on water? -OR - has anyone else ever experienced this problem?

 

Both batteries are used for starting, there's no isolation between them at all.

You need to unhook and load test both separately. If only one fails, you need to replace the pair of them together at the same time.

What's the float voltage of each battery?

 

Thank you - I was unaware of that. Had the truck since December of last year and haven't had a problem at all.

But this still doesn't answer the uphill/downhill portion of the equation. Just a coincidence?

 

Check the batteries first, electrical issues are so common on the 6.0 that it's worth ruling those out first. It won't be wasted effort or cost, no matter what the final result is. Plus if it is just the batteries, no need to go down the rabbit hole on all the problems you can find out about on the internet.

There's a specific forum for problems with this engine, you'll get more focused help there, this SD forum tends to traffic more in chassis/general platform problems and covers a lot more years and engines:
6.0L Power Stroke Diesel - Ford Truck Enthusiasts Forums

There is a general "no start" thread that covers common problems you can start reading:
https://www.ford-trucks.com/forums/8...condition.html

But honestly before you get to that point, the first thing pretty much anyone is going to tell you to do is buy a scanner. The most common is the Torque Pro app and an OBDII adapter. This is going to show you the data PIDs that 99% of the help you ask for will revolve around, there is very little advice around here that centers on blind part swapping and guess work. Discussed in this tread:
https://www.ford-trucks.com/forums/1...eral-info.html

Something like this:
https://www.amazon.com/Launchh-Inter...1P68SGFY3E7FN0

I'm really not sure about the positioning issue. It could be coincidental or it could be really bad. I could start listing out a bunch of things that it might impact, but they're all much more worse-case than a slow crank and a hard start.