Depth of Discharge Calculator
See how much of a battery bank you can actually use, and how depth of discharge changes the number of cycles you get.
Results
Nameplate capacity is not usable capacity
A 10 kWh lead-acid bank is a 5 kWh bank in practice. Draining flooded or AGM cells past half their capacity shortens their life sharply, so the usable half is the number that belongs in the system design.
The trade between depth and cycles
Cycle life falls as depth of discharge rises, and the relationship is steep. The same bank cycled to 80 % may last a third as long as one cycled to 30 %. Sizing storage generously is not waste: it is what buys the years.
Common mistakes
Buying a bank sized to nominal capacity. If the design needs 5 kWh of usable storage from lead-acid, the purchase is a 10 kWh bank, and that difference is the single most common reason off-grid budgets are wrong.
Questions people ask
Is it bad to fully discharge lithium? Less bad than for lead-acid, but not free. Most LiFePO4 banks are happiest cycling to 80 % and reserving the rest for emergencies.
What does a deeper cycle actually cost? Cycle life falls roughly in proportion to depth: cycling to 80 % instead of 50 % gives more energy per cycle but noticeably fewer cycles overall.