Battery switch

So I have been investigating the systems on our new to us 2003 Pilot II. Our old rig (26 Shamrock) had a battery selector switch allowing you to draw from the house, starting or both batteries at the same time. The Pilot just has one single pole switch below the sink in the galley to switch on and off the two batteries that are wired in parallel.I am surprised by this. My concern is running both batteries down if we were moored overnight. On the Shamrock I would switch us to the house battery with no worries the starting battery would drain down. Assuming they are in good shape how many hours do you think I have on the two paralleled batteries running the fridge, a light or two and maybe a small 12v tv knowing I need enough juice to crank the big Yanmar in the morning? thanks

regards Holty

No idea what a Pilot II is but I'd think you'd want a separate start battery.
Impossible to guess how long your current setup will run your loads without knowing what size battery. Still a guess since you don't know battery condition.

I'm with Sean, add a start battery and keep these as your house bank.
Blue Sea Systems makes a kit that makes adding a second battery bank and managing the charging pretty easy. https://www.bluesea.com/products/7649003/Mini_Add-A-Battery_Kit_-_65A_[Boxed]

I would add a separate start battery and use a simple Echo charger to keep it charged. Simple, cheap, and effective.

More data needed. Impossible to even give a good guess without knowing the size, age, and type of existing batteries. Also need to know the amp draw and approx duty cycle of the refer.
Big difference between a pair of old M27 starting and a pair of new 8D AGM!

"Our old rig (26 Shamrock) had a battery selector switch allowing you to draw from the house, starting or both batteries at the same time."

Duplicate this setup.

I know I need to separate the two batteries or add a third that is isolated from the existing two. Just surprised that Mainship wired it up this way. Maybe they assumed most buyers would go for a generator allowing the charging system to do it's thing.

regards Holty

They could have hoped the owner would only use one batt for Onite house service , and gotten started on the other if needed.

We use your system , but with propane refrigeration , the only house loads are a fan and car radio and lights, with an 8D as house batt.

It works , but one does have to be aware.