Battery Bank

A battery bank is a group of individual batteries connected together to form a single energy storage unit with the desired voltage and capacity for your solar system. Individual batteries are wired in series (to increase voltage), in parallel (to increase capacity), or in series-parallel combinations (to increase both).

For a 12V system needing 400Ah of capacity, you could connect four 12V 100Ah batteries in parallel — all positives together, all negatives together — giving you 12V at 400Ah. For a 48V system, you could connect four 12V 100Ah batteries in series — positive to negative in a chain — giving you 48V at 100Ah. For 48V at 400Ah, you would build four series strings of four batteries each, then connect the four strings in parallel.

Battery bank sizing depends on three factors: your daily energy consumption in watt-hours, the desired days of autonomy (how many days the bank can power your loads without solar input), and the maximum allowable depth of discharge. The formula is: bank capacity (Wh) = daily consumption × days of autonomy ÷ maximum DoD.

When building a bank, all batteries should be identical — same manufacturer, model, age, and capacity. Mixing different batteries causes imbalances where weaker cells limit the performance of the entire bank and degrade faster, creating a cascading failure pattern.

Higher system voltages (24V or 48V) are preferred for larger systems because they reduce current for the same power level, allowing smaller wire gauges and lower resistive losses. Most modern off-grid systems above 3 kW use 48V battery banks.