Chinook RV

I'm new to rigs with generators, but have a couple of related questions.

1) My engine battery was dead yesterday so I thought I'd use the Boost Start switch, but to no avail. Click in the engine compartment seems legit, but no bueno.
Also, the generator would not start. Is this normal?

Grabbed a dumb charger and charged the engine battery for a few hours and it started.
Testing today, it looks like it is at ~600~ CCA's
My battery (https://www.interstatebatteries.com/products/mtp-65) appears to have 750 CCA's when new.
Definitely suspect.

2) Generator starts and runs smoothly.
While running, disconnect the engine battery and the generator quits. Is this normal??

3) Because the Boost may use a smaller wire gauge, should I press-and-hold before attempting to start?

Thanks in advance!

An old post, but in case you still come back to check.

Yes, the generator starts off the engine battery. Doesn't seem like the best design, but it works ok with the boost button. The boost button needs to be held to "link" the house batteries to the chassis battery (like jumping from another car). Let go of "boost" once the engine starts. Once started, you can start the generator too. Generator charges the house bank first, then once it get's up close to full, will trickle over to the chassis battery.
That's a simplified explanation of the stock config anyway.