The two batteries may have different precharge resistor value. Try scaling precharge times differently in settings to compensate.
Have you used a scope to capture voltage at inverter, see what the RC time constant is and how close it comes to battery voltage? If it settles to a level below battery voltage due to DC current draw from inverter, or drops back down when load is applied.
Is it possible they would let you go onto a customer's property if you don't do anything on site, just "observe and report"?
A sales person could go to a customer's door, maybe come inside for a glass of water. He could hand over a sample.
Obviously turning a screw or flipping a switch is different. If a licensed (possibly insured) installer put in a replacement battery or tried to debug the problem, you could learn from what you see.
Companies of course usually have insurance to protect themselves from liability. In California, contractors aren't required to have insurance (except Worker's Compensation if they have employees.) They must certify they have "working capital" of at least $2000 (I suppose that was a big number when the rule was made), and a bond that is now $12,000.
One of the Net Metering x.x versions was going to require solar installers to carry $1 million insurance, and $1 million insurance on the horse they rode in on (vehicle insurance). Too many special interests getting their fingers on "all" the money that is made from PV. (Required automobile insurance in the state is/was $15,000 per person, $30,000 per accident, $5000 property damage. That would have been increased to $1,000,000 on the car driven to the job.)