Since the coach has been sitting the optima batteries that start her up were low.Tried a battery charger from a friend, which didn't do anything.
Bought the charger from Optima on amazon (https://www.amazon.com/gp/product/B009M3PQFA/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) and it took 4 days or so but all three are now in the green and she starts right up. When they put in the lithium system they must have disconnected the boost due to the different battery chemistries. Not sure. Since we didn't have the AC on, I didn't have her plugged in. I should install a charge cable from the Victron inverter charger to them, there is a 2nd charger for the start batteries.
Anyway if you have Optima batteries I recommend this charger. Worked great.
If you don't keep the coach plugged in, they will still (eventually) become discharged. Why not plug it in, if you have a way to do so?
If the coach is not plugged in the Victron Multiplus start battery charger will not charge the start batteries. The only sure way to prevent start battery discharge is to disconnect the start batteries when it is in storage. Or add a passive charger (solar) to charge the start batteries. You have a complex and expensive system that is likely unique (or certainly different from most FTs). Get the schematics and understand how it works. If you do not have detailed schematics then figure it out by looking and tracing wires and creating one. when you have a problem you need to know what and where to look.
Your Optimas may be compromised due to a very deep discharge. Be sure they stay fully charged. If your Optimas are wired as shown then move the center battery to one end or the other.
There is no reason not to have the boost solenoid connected and functional with lithium batteries for a short start assist. Just don't leave it on.
I have been using the Optima charger for 4 years now, works great. Remember to set it after you stop and plug in if you have it plugged in to your coach. I have mine plugged in under the bed and unit is attached to side of bed under the skirt. Out of the way and easy to read.
John
Even when not plugged in, I keep a small [36 watt] 3 stage agm charger on my start batteries.
This plugs into a small inverter I use to maintain the settings on the tv, sat and stereo. That way no problem with different voltages of lithium and agm batteries. I have a switch on the dash to turn it on or off.