Sizing
Lithium Battery Usable Capacity: Why We Assume 80%
We use 80% of nameplate capacity as a planning allowance, leaving a reserve. It is not a universal LiFePO4 limit; permitted discharge depends on the exact battery and its instructions.
Lithium Battery Usable Capacity: explanation
A battery may permit a different depth of discharge. The BMS cut-off is a protective limit, not the planned point for ending every trip.
Choose a reserve for essential loads, weather and ageing. For example, a 200Ah bank at an 80% allowance provides 160Ah for the runtime calculation.
More on sizing
How many amp-hours do I need on my boat?Add up every load in amps multiplied by the hours it actually runs, divide by 0.8 for lithium, and multiply by the nights you spend away from shore power.How long will a 200 Ah lithium battery last on a boat?About 160 Ah of usable capacity, which on a typical 38 ft cruising yacht drawing 149 Ah a day is a little over one night at anchor.