Me again i was spelunking aroundin Xentry and found this:

2550 what could be causing that?

 

Good find!
LAUNCH CodeReader shows that as well.

This internal resistance is a calculated value based on drop-voltage and current.

This is saying your AUX has an increasing hard time carrying load but not yet flagged as bad.

This is what battery drain does... basically lead/acid "sulfation".

When main AGM gets drained so does AUX!
AUX does not have any charge current limitation - Once flat it gets roasted by high current to meet ALT voltage.

The bottom line to prevent that:
CTEK Float charger on main AGM.

 

Dont you mean to recond the AUX battery?

 

Yes, you can try after removing the OEM AUX out in a safe place for venting.

Give it an "AGM Mode" deep-cycle battery reconditioning while disconnected from the car.

It won't hurt and may go another 5 years with normalized internal resistance value.

It's a small batt that needs a charger with small charge current option.

Anyway battery status is already going bad so nothing to loose before a replacement down the road.