Outback Power Systems FLEXpower ONE One Fully Pre-Wired Single Inverter System Installation Manual - Manual (Page 59)

Specifications
900-0095-01-00 Rev A
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Worksheet for Calculating Battery Bank Size
Use the following worksheet to calculate the battery bank size.
Table 8 Worksheet for Determining Battery Bank Size
Average amp-hours per day (from Table 7)
Divided by inverter efficiency
Divided by battery efficiency (usually 0.75)
Adjusted amp-hours per day
Divided by Depth-of-Discharge (usually 60%)
Multiplied by days of autonomy
Battery bank size required