With so many trucks with battery issues (and even if not), it’s REALLY unfortunate there is no true way for the owner to test a battery to know before hand if your battery is going bad. I’ve read many people who get their battery tested, even by a dealership for it to be tested okay, then completely fail right after. I known there are many ways to test a battery but nothing so definitive, and easy, that owners can use. Disappointing.
I've had the dealer test the battery and it "tested ok" even though it wasn't. A lot of them don't know how to test or anything about batteries. I came into the dealer this weekend. After 45 minutes on the highway, the truck was at 11.4V when we turned it on for the advisor to try to download the computer. I say try because he insisted it needed to be in accessory mode. I told him I'm pretty sure it's supposed to be in Run mode to bring up the interface. After a few minutes of it not downloading, we went ahead and did it my way and put it to Run (not started). Sure enough it started downloading immediately. Meanwhile, the battery voltage was down to 10.8V. (One of the issues for the visit was the constant run down of the battery). Told him at rate, you're gonna need to jump it to get it out of the service lane. The advisor told me oh it's normal, it's not about the voltage, it's about the cranking amps. Not a clue about them being related. Sure enough, they had to replace the battery (and do some software updates that address run downs). Just checked and after 3 days it's sitting at 12.3V. So either they gave me a crap battery (different advisor when I was picking up said they probably did), or there's still some drain going on (also likely given how much ghost draw there seems to be on these things)
Aside from interrogating the computer (it tracks battery capacity and state of charge), you can just look at the battery voltage on the dash when you first turn the truck off, or after it's been sitting for a few hours. A well functioning, fully charged AGM should be 12.8-13.2V right after you kill the engine. After a few hours in comfortable temperatures, it should be above 12.6. If you're below that you either have drain and/or the battery's on the outs.
After the recall update last winter, mine would drain it down to 11.8V within hours. There was an mid summer update that slowed that down to 12.2V, but still within a week down to 11.5. That's pretty much dead. Barely enough to turn the engine over.
Another indicator is to watch the voltage climb when you first start the engine. Good battery can absorb everything the alternator can throw at it, so you'll see it tick up to >14V. If it instantly gets there, battery's not able to absorb charge == bad battery.
Problem is the software can get OTA at any time. And if they push a bad update, it's bye-bye battery. Batteries do not like to get drained.