I'll be using my old cranking battery as my second battery until it dies.
I'll be running a small anchor light, stereo and depth meter (by default) from sunset to sunrise. This is for actually sleeping on the boat (my boating version of boondocking).
How will my old cranking battery fair as an overnight stereo battery?
Can it handle that draw for several hours? Or will I have a dead battery, just like if I left the car lights on all night?
If I get a group 27 marine/rv deep cycle instead, and my old starting battery finally fails, will I be able to use the marine/rv deep cycle to start the boat until I get a new cranking battery?