Battery life...

I have both Webasto engine and bunk heater. Ten hours at -20F the truck still starts fine.
I also have an inverter that runs my apartment size refrigerator.
My last truck had AGM batteries, they didn't have as good reserve capacity.

 

AGM batteries need a different type of regulator on the alternator to prevent them from being messed up. I had them in my pickup, went through two sets within a couple years while the originals lasted 6 years, so I called Optium and talked to one of their techs, telling me he was surprised it lasted that long and he said to go to a Balmar programmable regulator. This last set has been in both pickups for the last 8 years.

 

You're new and they're jumping on you about idle time. So don't idle the truck. If you need to do so then certainly do so, but not on some abstract fear of needing a jump start. They're telling you conserving fuel is a greater priority. They aren't particularly concerned about needing a jump start because power is automatically shutoff once the voltage drops to 12.3v. If the batteries are good that's plenty of juice to start the truck.

If you actually had to do what you believe it wouldn't take long before you failed to do it and you needed a jumpstart. It wouldn't take many of those before you decided you might as well just leave it running. That's what millions of drivers already did. So they came up with better solutions. The cheapest is just a low voltage cutoff. Some trucks will start automatically and idle when the voltage gets low, recharge the battery and shut back down. Some have separate battery systems for starting. Some have separate generators (APU). All better solutions than counting on the driver to keep the battery charged.

 

I can't charge my bracelet anymore. Today I took it apart and found the bracelet battery bulge. By the way, I found the battery inside a Bluetooth headset and changed it. It is still charging…

 

Exactly
I also get away with idling because i have a CPAP and dead batteries is not an option for me, so they say nothing and deal with it
APU use FAR LESS fuel then idling but are expensive to install so catch 22