80k maintenance & then ECM relay went...could this be related?

Hello,

I don't really know much about how my diesel works...unfortunately. I have had all my work done at a dealership until the 80k scheduled maintanence.
Local dealership closed - so off to a often referred "motorsport" shop. Here is a layout of what happened:

1. Had new key and existing key re-coded at dealership a week before shop work
2. Shop did regularly scheduled 80k work
3. At construction stop one week and about 300 miles later- car would not start
4. Every warning light went off
5. Engine clicked but would not turn over
6. Battery pack was put on and battery showed full power
7. Towed to shop and the next day the OTHER key started car BUT still lots of warning lights on
8. Shop had to replace the ECM power relay

Now one week later, the engine cranking has gotten progressively worse - at last try today it barely started and I am expecting to have to jump it tomorrow to get it going. Set to go back to shop to have battery tested.

My question: Could the 80k work or re-coding of the keys been the catalyst to the ECM power relay issue and or perceived battery issue?

I want to trust this shop but have no knowledge base to connect the two situations if in fact there are dots to connect.

Any feedback is greatly appreciated!