Battery Size Calculator

Your details

Choose whether you know the load as a wattage or as a current draw.
Total wattage of everything the battery will power.
W
Nominal voltage of your battery bank.
How long the battery must power the load without recharging.
hours
Chemistry determines how deeply you can safely discharge (DoD) and how efficiently charge cycles convert energy. Lithium chemistries tolerate deeper discharge and have higher round-trip efficiency.
Extra headroom above the calculated minimum. A 20% margin means you buy a battery 20% larger than the bare minimum, protecting against unexpected extra load, temperature dips, and cell aging.
%
Required capacityGentle discharge (C/10)
51.5Ah

Minimum usable capacity after DoD and efficiency losses

Energy required480Wh
Load current5A
Rated capacity with margin61.9Ah
C-rate0.097
Depth of discharge (DoD)1%
Round-trip efficiency1%
0.097 C
Gentle (C/10)<0.1Moderate (C/5)0.1-0.2Fast0.2-0.5Very fast0.5+
Min capacity (Ah)51.5
Recommended (Ah)61.9

You need at least 51.5 Ah (61.9 Ah with margin) for a 8-hour runtime.

  • A lithium-ion battery can be discharged to 80% DoD, so you need 51.5 Ah of rated capacity to deliver the required energy.
  • With a 20% safety margin for aging and temperature variation, look for a battery rated at least 61.9 Ah.
  • Your discharge rate is C/10, which is gentle and will help the battery deliver its full rated capacity.

Next stepLithium batteries also lose some capacity in the cold, though less than lead-acid. Store and use above 0 degC (32 degF) where possible, and avoid charging below 0 degC to prevent lithium plating.

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