Anyone here know enough about the ECO battery, BMS and high speed canbus networks to comment on the following?

Have had multiple ECO batteries replaced in warranty and finally gave up over 2 years ago when it went out of warranty. The ECO battery has been placed on charge several times but nothing has every been able to bring it back from the dead so I just ignored it.

Two years later, over the past month or so, I have had numerous high speed canbus lost communication DTCs, sometimes with ALL modules on the network failing, causing a variety of side effects such as no speedometer, no shifting (stuck in 1 gear, stalling, etc). I tried a variety of trouble shooting steps as well as SDD but came to no conclusions so I gave up and brought it to the main dealer. I explained everything in detail and was told they would need a substantial diagnostics fee to have a look.

A day later they rang back and advised that while there are tons of DTCs, nothing is telling them specifically what needs to be done other than the dead ECO battery I had already told them about. They said I need to replace it but can't guarantee that has anything to do with what's wrong with the car. I insisted that makes no sense as why would it be fine for 2 years and only now have canbus errors. The response was even new cars have the same problems and you just have to live with them......

So, any thoughts?

EDIT: I also have been monitoring alternator voltage and frequently observe voltage spikes in the 15-16-17 volts & higher range.