Recently, after the truck sat for 8 or 9 days while at a campground and it was about 31 degrees (after a 22 degree low and snow) I couldn't get the truck started. The batteries went very low after only a few tries. Finally, I got it going with my Walmart marine battery I use for a house battery for my camper. I had both batteries tested at O'reillys in the next town (they started it the next morning at around 40 degrees out, but still seemed weak) and their tester in the back area said both were good under load. My alternator and voltage regulator are about a year old and are putting out proper volts, so we can rule that out. After sitting 4 days, I found the batteries around 12.3-12.4 before trying to start it. I will be tomorrow. I ran my generator's 5A built in dumb charger for about 5 minutes and they showed 12.8 but of course that was a float charge or whatever before they settled down. Sounds like I either have bad batteries, or something is pulling power while parked that didn't used to. Does that sound typical of dying batteries? Every other time batteries have died on me in gas vehicles, they seemed to just totally die all at once, less "kind of dead" like this. Maybe it's because if these were in a gasser, there wouldn't be symptoms yet since there's no glow plugs to strain them before cranking.