Series and parallel wiring calculator

Pick batteries or solar panels, then how many go in each string and how many strings sit side by side. The diagram redraws as you type, and you get the resulting voltage, amp-hours or current, energy and power, with a check against the limits the makers give.

Inputs

Each string joins this many units positive to negative. Series adds voltage.

This many identical strings are joined positive to positive and negative to negative. Parallel adds capacity or current.

V

A "12 V" lithium battery is 12.8 V nominal; lead-acid is 12 V.

Ah

Use identical batteries: the same model, capacity and age.

A

From the data sheet. Parallel strings add up; series does not.

Bank voltage

25.6V

2 strings of 2 in series, 12.8 V each and 100 Ah.

2 strings of 2 in series make a 25.6 V bank of 200 Ah. Every part of the system (inverter, charger, charge controller) must be rated for 25.6 V.

Capacity
200 Ah
Energy
5,120 Wh
Max continuous current
200 A
Max continuous power
5,120 W
Batteries
4
Battery bank wiring: 2 strings of 2 in series

Bank output 25.6 V · 200 Ah

−+12.8 V100 Ah−+12.8 V100 Ah−+12.8 V100 Ah−+12.8 V100 Ah−+

Along a string the voltages add and the amp-hours stay the same. Across strings the amp-hours add up and the voltage stays the same. The output leads leave from opposite corners so every string carries the same current.

2 strings of 2 in series: the voltages add to 25.6 V and the capacity is 200 Ah (5,120 Wh). The bank can deliver up to 200 A continuously. The drawing shows each battery as a box, joined plus to minus along every string, with the strings joined at a bar on each side and the bank’s output taken from opposite corners. 2 strings of 2 in series make a 25.6 V bank of 200 Ah. Every part of the system (inverter, charger, charge controller) must be rated for 25.6 V.

Safety first

A battery bank can deliver hundreds of amps into a short circuit, and the amp-hours add as you put strings in parallel. A series bank has a higher voltage than the system around it was built for.

  • Fuse every circuit, including each series string of a parallel bank (Victron) and the main cable at the battery. The fuse protects the wire, so it must not be bigger than the wire’s rating.
  • Follow the manufacturer’s instructions for the batteries and every part of the system, including the limits on series and parallel connections. The inverter, charger and charge controller must all be rated for the voltage you build.
  • Follow your local electrical code and any marine or RV standard that applies to your vehicle or boat.
  • Have a qualified person check the installation before you switch it on. Charge each battery on its own to the same level before you join them in series.

How it works

voltage  = units in series × voltage of one unit
capacity = strings in parallel × amp-hours of one unit     (panels: current)
energy   = voltage × capacity = units × volts × amp-hours
  • A string is the units in series. The bank is the strings in parallel.
  • Series joins the positive of one unit to the negative of the next. The voltage adds, and the current stays the same.
  • Parallel joins all the positives together and all the negatives together. The current adds, and the voltage stays the same.
  • Panels work the same way with Vmp and Imp. The open-circuit voltage adds in series and the short-circuit current adds in parallel, and those two figures set the charge controller and the fuse.
  • The drawing shows the output leads at opposite corners, which both Battle Born and Victron recommend so every string carries the same current. Long strings and wide banks are drawn with a gap, but the totals are for the whole bank.

Worked example

Four 12.8 V, 100 Ah lithium batteries, each good for 100 A continuously.

  • Two strings of two (2S2P): 25.6 V, 200 Ah, 5,120 Wh and up to 200 A. This suits a 24 V system.
  • Four in series (4S): 51.2 V, 100 Ah, 5,120 Wh and 100 A. This is the limit Battle Born and Victron give for 12.8 V batteries.
  • Four in parallel (4P): 12.8 V, 400 Ah, 5,120 Wh and 400 A. The same energy, at the highest current.
  • The same four batteries always hold 5,120 Wh. Only the voltage and the current change, which is why the right layout is the one your inverter, charge controller and cable want.

Tips from the road

  • Charge before you join. Both makers say to bring every battery to the same charge before wiring them in series, and Battle Born suggests about 14.4 V each.
  • Fuse each string of a parallel bank. If one string shorts, the others feed it. A fuse on each string limits the damage.
  • Keep the cables the same length. A longer path has more resistance and carries less current, so the batteries near the output work harder than the rest.

FAQ

What happens when you wire batteries in series?

The voltages add and the amp-hours stay the same. Two 12 V batteries in series make 24 V, four make 48 V, and each string still holds the amp-hours of one battery (Battle Born). The energy in watt-hours adds up either way, because the voltage rose while the capacity did not.

What happens when you wire batteries in parallel?

The voltage stays the same and the amp-hours add. Two 12 V 100 Ah batteries in parallel are 12 V and 200 Ah. Battle Born adds that the main connections should be taken from opposite ends of the bank, with equal-length cables, so every battery shares the load.

Should I wire solar panels in series or parallel?

Series adds voltage and parallel adds current, so the total power is the same. Series is good for long cable runs because the current is lower, and parallel for a 12 V system (Renogy). Renogy also says MPPT controllers suit panels in series and PWM controllers suit small, voltage-matched arrays. Always check the series string's open-circuit voltage, on the coldest morning, against the controller's limit.

Can I mix batteries of different sizes or ages?

Avoid it. Victron says that a 50 Ah battery in series with a 100 Ah one gives a string of 50 Ah, and over time the imbalance cuts the capacity further. Battle Born says to use the same model and capacity throughout and not to mix batteries of very different ages.

How many batteries can I connect?

It depends on the maker. Battle Born's standard batteries go up to four in series (48 V). Victron allows four 12.8 V batteries in series and 20 in the whole system. This page warns when a bank goes above 51.2 V or 20 batteries; your battery's manual is the limit that counts.

Sources

  1. How to Wire Batteries in Series, Battle Born Batteries. Two 12 V batteries in series are 24 V and four are 48 V with the amp-hours unchanged; the most for standard Battle Born batteries is four in series (48 V); charge each to about 14.4 V first; series strings can be paralleled to add capacity.
  2. How to Wire Batteries in Parallel, Battle Born Batteries. Two 12 V 100 Ah batteries in parallel are 12 V and 200 Ah; take the main connections from opposite ends of the bank; use equal-length cables and matched batteries.
  3. Lithium Smart Battery manual, sections 3.1 and 4.5, Victron Energy. Up to 20 batteries in one system; a maximum of four 12.8 V batteries in series; 20 in parallel, 2S10P or 4S5P of 12.8 V/330 Ah is 84 kWh; fuse each series string; connect the system cables diagonally.
  4. MPPT solar charger manual, section 4.3, Victron Energy. Series, parallel and series/parallel panel arrays drawn with 120 W 12 V panels (240 W 24 V 10 A, 240 W 12 V 20 A, 480 W 24 V 20 A); take Voc and its temperature coefficient into account when counting panels in series.
  5. Solar Panel Wiring Basics, How to Wire Solar Panels, Renogy. In series the current stays the same and the voltage adds; in parallel the voltage stays the same and the current adds; power is voltage times current.

Formula and sources last checked September 30, 2026. How we test formulas.

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Safety note: Estimates only. Equipment ratings vary by manufacturer, so always follow the manufacturer’s instructions and ratings, and ask a qualified professional when safety is at stake.