Well, I replaced the instrument cluster illumination lights yesterday ('00 F250), just with the stock 194's since the console was very dim.
This morning went to start and the battery acts dead, turns over a quarter turn and then clicks as if dead.
Didn't leave any lights on over night, only got down to 56 (Michigan).
Batteries show 12.2v but (poor quality meter). Jumped with new truck, no drwa noticed when I connected them. Waited several minutes, same thing, except I also noticed the windshield wipers slowly going through a cycle (they're off).
I have a 200amp load tester built in my Century commercal battery charger. Comes in handy. I had a battery, several months ago, that tested 4 bad cells. Before that, I discovered some charging problems with the alternator because the hydrometer readings were showing int the 50-75% charge range and wouldn't build beyond that. Fast forward to new batteries and alterantor...never started so good in a long time. The original alternator was charging, but not at full capacity.
Cleaned the battery cable connector's/terminals, no change. In fact worse. With key in the run position, but before turning to crank, chimes and lights flash off and on, relay switching under the dash. It's like a constant cycling of the key from off to run.
With this coinciding with having the instrument console out, it seems like I did something in there.
The confusion you experienced is common when using lead-acid "flooded" batteries.
There's more to the equation than just voltage, and that's available current.
Just as important as "charge-state" is "reserve capacity".
Reserve capacity diminishes over time, and at end-of-life, a battery may still be capable of producing its full 12.6 volts, but it's effectively the size of one of those small batteries you see as a back-up in alarm systems. At that point, it's not capable of producing the amperage necessary to start the truck.
The reduction in reserve capacity is caused by the battery's plates getting covered by sulphation. That forms on the plates anytime the battery gets below about eighty percent of fully-charged, and is only partially reversible. As a result, the battery will last the longest if you keep it as fully-charged as possible during its entire life.
But, there will always be an end-of-life. How far in the future depends on a few things, but charge-state is one of the biggies. If I were not driving mine daily, I would have a float-charger on it. Additionally, an "equalization charge" is desirable every six months or so to "top it off".
But good care only extends the time at which your batteries WILL die, and you found out when!