Trouble shooting steps
Mine is an early model, but assuming your backup battery is the internal one for the D180 (call it the D180ib) my troubleshooting by web hunch is that the D180ib needs to be replaced. No matter you get 14.6VDC (actually shouldn't the D180 IB display 16.2 or some such?). Replacing the D180ib is a quick relatively inexpensive test that if nothing else will leave you with a new spare D180ib. Moving on... Simply remove or replace the D180ib and see if the problem goes away or remains. If problem remains you know it is not the D180ib. Now pull the D180 and bench power it to see if the problem still stays with the D180. If you need to simulate conditions, stick it in the fridge for a day and then test again. If the D180 passes your bench test then, for the moment, you can assume the D180 internals are OK. Were are we? The D180 and D180ib have been checked. This leaves the RV wiring. Start by checking the connector pins on both the D180 and its wire harness. Make sure they are flush with each other and not bent and or recessed. Next check the connector for pins that didn't seat fully. I can do a tug on each of mine but my unit is one of the very early models. Next, using an ohmmeter (continuity checker) and extra wire test each related wire in the harness from beginning to end point. You should have pin connector diagram for your unit. Given what Dynon charges, the key is to be sure as much as possible that your D180 does in fact have a problem before sending it to them. I believe my suggestions will help you with that.