Solar power notes.
So. what is a deep cycle battery? A lead-acid battery that is designed for deeper discharges, but that means to 50%, not to 0%. Normally lead-acid batteries are used for car starters (well, at least the vast majority still in use as of 2018) and do not go through such deep cycles.
20180628/DuckDuckGo deep cycle battery
20180628/https://en.wikipedia.org/wiki/Deep_cycle_battery