It's been my experience and the wisdom I've received that most vehicles don't fully top off their batteries. From my reading the best thing you can do for longevity is to plug in a battery tender every now and again.Which I find interesting as if these were any other batteries or vehicles, I'd be trying to figure out why the batteries never fully charge with the system voltage running over 14 volts while running. Mine runs 14.5 and higher much of the time, that's well into the rage to fully top off an AGM battery.
And while it cranks and works fine even when it's 0 outside, 12.3 is not a fully charged battery.
When searching using Bing or Google and looking for things like "what is the voltage of a fully charged AGM battery" you always get 12.6 or better and even thought SoC charts don't agree on exact numbers, they all agree - 12.4 or less is only partially charged, the best chart saying 75% while the worst saying 60% charged at 12.3 volts.
So, automotive EEs here - what's up with this? I can go to my cars any time and find the batteries even after sitting 2 to 4 weeks have a charge of over 12.5 volts and those start out at 12.6 while a full AGM starts out higher.
In short - why aren't Jeep vehicles fully charging AGM batteries, or, are all of the battery companies - those that MAKE and sell AGM batteries, full of bunk when they say that 12.4 isn't fully charged?
Someone is not telling the truth.
In any case, my ESS only works when the truck is driven for hours, or I charge the batteries overnight, otherwise, the batteries sit at 12.3 volts or LESS and the ESS doesn't work with a battery charging message.
And this shows the voltage with the battery under a load ->
So one could explain a measure of 12.5 volts at the terminals away if there's a fair draw on the battery at the time. It would still be 100% charged IF there was a load like shown here - but mine measured 12.25 volts (and less) so even assuming there's a discharge on it to keep the truck in listen mode, it's still only 80% charged!
On my Triumph Tiger my dealer thoughtfully installed an SAE pigtail for easy charging and accessories. I plan to do the same on my JT. Aerostich sells an sae cap/ voltage meter that let's me check SOC with a button.
My bike for instance has a key transponder that is always on and draws some current. The JT's are worse with the remote start and unlock receiver always online. Then you have the UConnect vehicle location and status connection sending 4G data meaning the transceiver and computer need to run periodically. All of these devices together can drain your battery over time.
One thing I dislike about ESS is that if you are only taking shorter trips, the restart consumption may exceed the recharge input during a drive cycle. So over time you can get a net loss of charge, hence a trickle charger being important.
A few weeks after purchasing the JT I put a battery tender on and it took over 12hr to show full charge. Interestingly, after charging I got an ESS error for the first few drive cycles. I subsequently learned that the system looks for a level charge between the main and alt batteries. Because I hooked the charger to the main battery I figure it created a charge disparity that triggered the warning. That it stopped triggering tells me that the ESS battery was able to come up to the main charge state during those drive cycles. Henceforth I plant to attach the charger to main positive and the ground bus to see if it also charges the alt battery.
To sum it up, battery tender, battery tender, battery tender.