I’ll stipulate up front that I know electrical setups vary wildly between specific boats. That said: I’m about to do a weekend charter on a 36 ft sailboat, and I was wondering if there is a general amount of time that is typical to run the engine per day to top off the house bank.
I imagine it depends on the type of battery and the usage, but if you have a battery meter you could measure it. Use the house bank for a day, measure the voltage, run the engine for an hour, measure it again. Looks like the number you want to get to is probably 12.8 V: https://naturesgenerator.com/blogs/news/lead-acid-battery-voltage-chart