Promaster 3500 cargo van battery problems and PCM failure

My 2015 diesel cargo van has been having issues with the battery dying and
the PCM reading multiple faults since its purchase in 2016.  The dealer just
told me to cycle it through a few starts and the computer would clear itself.  
Also, the van needs to be run frequently so the battery doesn't die.  I
replaced the original battery at 10K miles....still issues, and have to put on a
trickle charger 24/7.  Finally, it died for good.  It has been at the dealership
for 3 months.  The repair guy said it was a bad battery cable connection, and
it screwed up the PCM.  It is undrivable without the PCM, which has been on
order for over 3 months.  Every two weeks someone contacts me and says it
won't be in for 2 more weeks.  The date now is 4 months after I originally
brought the van in for service.  I'm sure it will change to a future date again.  
I'm not sure if I will ever get my vehicle back.  How do I handle this?  It has
less than 25K miles on it.