Another view.....

The chassis batteries are not charged when the bus is connected to shore power unless you have a provision for charging.

However, despite what some may experience our two coaches never required charging between use or shutting off the chassis main switches. We have gone as long as 3 months with no noticible loss of chassis battery starting power without maintaining the charge or turning off the master switches.

I would suggest if the chassis batteries are losing power over a short period of time you have a phantom load that needs to be identified and possibly corrected.