The rules
Series: voltages add, Ah stays the same
Parallel: Ah add, voltage stays the same
Energy (Wh) = bank voltage × bank Ah
Examples
- 2 × 12 V 100 Ah in series = 24 V 100 Ah = 2,400 Wh.
- 2 × 12 V 100 Ah in parallel = 12 V 200 Ah = 2,400 Wh.
- 4 × 12 V 100 Ah, 2 series × 2 parallel = 24 V 200 Ah = 4,800 Wh.
The total energy is the same however you wire them. Series wiring just trades amp hours for voltage, which cuts current and cable size.
Good practice
- Use identical batteries: same make, model, capacity and age.
- For parallel banks, take the main positive from one end of the bank and the main negative from the other end ("diagonal" wiring), with equal-length links, so every battery shares the load evenly.
- Fuse each parallel string, especially with lithium batteries.
- Check that lithium batteries are rated for series use. Some have a limit on how many can be connected in series.
Frequently asked questions
Do two 12V batteries in series make 24V?
Yes. Two 12 V batteries in series give 24 V with the same amp hour rating as one battery.
Does wiring in series give more power?
It gives the same energy but at a higher voltage, so the same power needs less current. That's why larger systems use 24 V or 48 V.