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Battery capacity must cover the load energy, grossed up for inverter and round-trip losses and then divided by the usable depth of discharge, since discharging a lithium battery fully shortens its life. The resulting C-rate — power divided by capacity — must be within the cell's continuous discharge rating.
Battery sizing
Nominal capacity = load power x hours / system efficiency / depth of discharge
C-rate
C-rate = load power / nominal capacity
Lithium battery installations present fire and thermal runaway risks and must comply with the applicable electrical and fire safety standards, including ventilation and separation requirements.
Modern lithium iron phosphate systems allow 80-95% with acceptable cycle life. Lead-acid should be limited to 50% for deep-cycle duty, which doubles the capacity needed for the same usable energy.
High discharge rates cause voltage sag, heating and accelerated degradation. Systems designed for short high-power bursts need different cells from those designed for long slow discharge.