There should be no corrosion on AGM battery posts. I never see corrosion on AGM battery posts, ever. This is noted on my Yamaha quad, the RV house batteries, the Ecodiesel too (sold). My Cummins isn't old enough to have this issue, yet.
I'll attach a pdf with very good info on how AGM batteries work. I used this info to set up my solar array with AGM batteries.
Under normal operation they should NOT leak anything. You can even lay AGM/Gel batteries on their sides. Charging voltages need to be turned down a bit from what a regular wet cell battery can use. You can overcharge AGM batteries, they can swell up and blow off gas, there is a relief valve. That old style 30 year old battery charger will kill AGM,s.
If the post is leaking gas, and I think it is, eventually the electrolyte will evaporate off, and with no way to replenish, and will fail prematurely.
The Duracell AGM house batteries on our RV are 3 years old now, and have zero corrosion. These batteries are depleted every night when we're out and about, and are hard charged during the day via 4 100 watt solar panels, and are worked very hard. Zero corrosion. The old wet cell style batteries were another story, I was always adding water and cleaning off the posts.
Is there corrosion on the the other battery? (The Cummins have two for those not in the know) I never noticed any battery corrosion on my Ecodiesel after 3 years.
I suspect
@Captainmal you just have a defective battery. I hope that is all the issues you have with what is so far for me, an outstanding solid truck! Good luck on that HPFP replacement!