Series vs parallel
Batteries in series add their voltages; the amp-hours stay the same. Batteries in parallel add their amp-hours; the voltage stays the same. A bank is built from identical series strings connected in parallel.
Batteries per string = System V ÷ Battery V
Strings in parallel = Target Ah ÷ Battery Ah (round up)
Target Ah = Target kWh × 1,000 ÷ System V
Example: 10 kWh at 48 V from 12 V 100 Ah batteries
4 in series makes 48 V. 10,000 ÷ 48 = 208 Ah, so 3 strings (300 Ah). Configuration 4S3P, 12 batteries, 14.4 kWh.
Tips
- Use identical batteries of the same model, capacity and age.
- Lithium batteries need BMS support for series connection; check the maximum number allowed in series.
- Fewer parallel strings is better: current sharing and balancing get harder beyond 3–4 strings.
Frequently asked questions
How many 12V batteries make 48V?
Four in series.
Can I mix old and new batteries?
It isn't recommended. The weaker battery limits the bank and wears out faster.
Is it better to use one big battery or several small ones?
Fewer, larger batteries simplify wiring and balancing. Several smaller ones give redundancy.