A green eye in the battery is good, red means bad. Eye was starting to show some green around the outside edge, good sign.

 

It's basically a floating hydrometer in cell 2 of the battery, if the specific gravity dropped so much that the floating ball sunk then that's your 'black' eye you see through the peep-hole. Since it's only in cell 2 it doesn't replace doing a proper specific gravity test manually with the tops popped off since there could be other bad cells in the other 5.

I wish they made automotive flooded batteries like the industrial batteries that I deal with... they have a clear casing so you can inspect the electrolyte level and plates and see how much plate material has fallen off onto the bottom. Bent or cracked plates are easily visible this way.

 

The red eye in the battery never went away. I bought a battery hygrometer and tested the battery. It confirmed the red eye. I disconnected the new battery and tried starting the truck with the original battery. Truck would not start. I also tested the new battery and hygrometer said that was also bad! I used the hygrometer to test the batteries in my pickup and they were good, so the hygrometer was fine. I stopped by the dealer and showed the service advisor the hygrometer tests. Truck was starting fine so not much he could do. Yesterday after sitting for 2 days, the truck would not start again. I called the dealer and he had the truck towed to the dealership without jump starting it. I had called Fords customer service at his recommendation to get the second battery replaced and Ford had been in touch with him. He said they are finding an intermittent draw problem on some trucks and will open a hot case.

 

I've got a 2012 F350 Lariat doing the same thing. Initially thought it could be my sub amp (not on a switched circuit yet) but pulled the fuse to that and had the same problem. Not home now but when I get there this weekend, will check what the draw is in Key Off.

 

The batteries went dead again. Dealer had the truck towed to the shop without jumping it. They tested both batteries and they are good. The tech happened to be walking by the truck and noticed the radio light was on. He thought the radio was bad so he ordered a new one. When he contacted Ford to tell them what he found, the engineer on the phone said it was not the radio, but the radio was the weakest ground in the truck and something else had a bad ground and was turning on the radio light. They spent today on the phone with Detroit trying to pinpoint the problem, but where unsuccessful. The regional super trouble shooting tech has been called and will look at the truck, hopefully this week.

 

I sure hope for your sake the "super tech" figures it out.
If it's a ground, which it sounds like it is, I don't imagine that will be an easy find.

 

parasitic electrical draws and bad grounds are tough to figure out. I usually will confirm what the parasitic draw is isolated to by putting a volt meter on the battery and pulling fuses until I find the guilty circuit (see the video for explanation). In the past, it's usually the radio and it's usually something I've done to cause it as I have done a lot of custom audio wiring. Every time I've tried to save a step, it bites me so I started wiring all new and these types of problems went away.

Anyway, the service tech will likely perform this type of test in diagnosing the problem (unless they have a better way, but sometimes low tech works well). Once they isolate which circuit it is...they need to trace the entire circuit. It's time consuming and not that easy. I'm sure none of this is "news" to you, but it's likely a chaff or cut somewhere and it's causing you a lot of grief. Sorry...I hope they can figure this out soon.

 

i bought. F550 tow truck flat bed and the battery keep going dead every 2days.
NTB now refuses to swap the battery under warranties, reasons because they've changed the battery twice in a week.
they advice I go check what was draining my battery.
please help!

 

Parasitic draws are a tough one to answer on the web. You've eliminated the battery, and these trucks don't have any offenders for causing battery draws that comes to mind.
If your not comfortable with a multimeter, this will be tough to fix on your own. If i was going to throw a dart, I'd start with upfitter added stuff. 2 days is a long time for most tow trucks to sit idle, and the previous owner may have just ignored the problem, if he was even aware of it.

 

It could be a bad alternator. Have it tested