06 Volvo S40 awd 2.5T no crank, no start, no cluster light check, MIL[FIXED]

Hey people, so as the title reads, I'll try to bullet point this.
First visit at my shop, customer complaint of wet passenger floor and blower motor consistently running, even when vehicle off and locked. What was found, coolant pipes to heater core leaking and heavy corrosion on plug B of CEM.
Repair Changed piping and heater core unit with factory parts, and CEM was sent out and replaced with clone.
Made repair and also found lower radiator hose leak at T-junction.
Vehicle came back for hose and new complaint of passenger foot well light staying on for an hour at a time.
Replaced hose and removed bulb per customers request, finished and parked vehicle outside.

Now went to restart vehicle to check coolant level, and vehicle was died. grabbed jump box, and got s40 to start.
Brought it inside and afterwards wouldn't so much has crank. no linking from starter relay, nothing.
What I've checked I'm showing all proper voltages from SCU to CEM. Only pending code is CEM-1a41 for fault or short between SCU and the CEM. Tried factory SCU and no change. So I went and physically jumped stater relay with power probe to check starter function and starter motor is fine. What I noticed is that I have Both batt powers to relay plug, they come from CEM. But I don't have grounds in plug, which I believe the ECM grounds.
Finally I had battery on 2amp charge over night and hooked battery back up and I had everything, crank, started, and cluster lights.
I'm not trusting that it's just the battery, any help would be appreciated.

Update

Vehicle had wrong group class battery for a previous year. Installed correct battery and everything appears to be functioning correctly. The wrong battery tested at around 400 CCA so I'll be marking this one fixed and returning to customer.

Thanks for the update