The Series / Parallel Battery Calculator shows how an identical-battery bank changes when you place batteries in series, parallel, or a series-parallel arrangement. Enter one battery's nominal voltage and amp-hour rating, choose the number of batteries in each series string and the number of parallel strings, and instantly estimate bank voltage, total Ah, nominal Wh, usable energy, and total battery count.
Use it to compare layouts before planning an RV, marine, solar, off-grid, or backup system. The math is simple, but the finished bank must still match the inverter, charger, BMS, cable, fuse, and battery manufacturer's connection limits.
Model an equal-string battery bank and see exactly what series and parallel wiring changes. The calculator keeps nominal ratings, usable depth of discharge, and system efficiency separate so the result is easier to interpret.
A series connection increases bank voltage while the amp-hour rating of one string remains the same. A parallel connection increases bank amp-hours while bank voltage stays the same. Combining the two lets you raise both voltage and capacity. If your goal is to size a bank from daily energy demand rather than from a chosen layout, start with the Battery Sizing Calculator; if you already know the layout and need cable planning, continue with the Wire Gauge Calculator.
This model assumes equal series strings built from batteries with the same nominal voltage and Ah rating.
The Series / Parallel Battery Calculator applies two basic electrical rules. Series adds voltage. Parallel adds amp-hour capacity. A series-parallel bank uses both rules while keeping each parallel string electrically equivalent.
Think of a battery bank as a set of identical building blocks. In series, the positive terminal of one battery connects to the negative terminal of the next, so the voltages add along the string. In parallel, complete strings share common positive and negative connection points, so their capacities add while the string voltage stays unchanged. The bank's ideal nominal energy is the sum of the energy stored in every battery.
This distinction is useful when choosing between 12V-, 24V-, and 48V-class systems. For a fixed power level, higher voltage means lower current because current is approximately power divided by voltage. Lower current can make high-power system design easier, but it does not remove the need for correct conductor and fuse sizing. Use the site's 12V lithium calculator, 24V calculator, or 48V calculator when you want voltage-specific runtime and capacity planning.
A practical workflow starts with the voltage required by the inverter or DC equipment. Divide the desired nominal bank voltage by one battery's nominal voltage to see the series count that would be needed. For example, 25.6V divided by 12.8V gives two batteries in series. The result must correspond to a real whole-battery configuration that the product manufacturer approves; the Series / Parallel Battery Calculator cannot make an incompatible voltage combination valid.
Once the voltage is chosen, every charger, inverter, monitor, disconnect, and DC load connected directly to the bank must be suitable for that system voltage. This is one reason voltage selection usually comes before simply adding more batteries.
After the series count establishes bank voltage, estimate how much Ah or Wh you need and divide that requirement by the capacity of one complete series string. Round up to a whole number of equal parallel strings, then verify that the charging system can restore the larger bank within the time available.
Extra parallel capacity can improve runtime, but it also increases stored energy and available fault current. For solar projects, compare the finished bank against expected daily production with the Solar Battery Calculator rather than sizing storage in isolation.
For identical batteries, each added battery in one series string adds its nominal voltage. The string's Ah rating remains the same as one battery. Two 12.8V 100Ah batteries in series are modeled as 25.6V 100Ah.
Check battery voltage guidanceFor equal strings, each added parallel string increases amp-hour capacity while the bank voltage stays unchanged. Two 12.8V 100Ah batteries in parallel are modeled as 12.8V 200Ah.
Convert Ah, Wh and kWhBuild equal series strings to reach the required voltage, then place those strings in parallel to add capacity. Four 12.8V 100Ah batteries arranged 2S2P are modeled as 25.6V 200Ah.
Review battery wiring guidanceEvery result can be checked by hand. The formulas below use nominal ratings and assume identical batteries with equal series-string lengths.
If one battery is 12.8V 100Ah and the layout is 2S2P, bank voltage is 12.8 × 2 = 25.6V, bank capacity is 100 × 2 = 200Ah, and total battery count is 2 × 2 = 4.
For the same four 12.8V 100Ah batteries, nominal energy is 12.8 × 100 × 4 = 5,120Wh regardless of whether the layout is 1S4P, 2S2P, or 4S1P. Wiring changes voltage and Ah distribution, not the sum of ideal nameplate energy.
The usable-energy estimate is deliberately separate from nominal energy. Depth of discharge represents the share of battery energy you plan to use. System efficiency represents estimated energy lost between the battery and the load. Those are planning assumptions, not universal product specifications. If you want to turn the final usable Wh into a runtime estimate for a particular load, use the Battery Runtime Calculator. If you need to estimate recharge duration afterward, use the Battery Charge Time Calculator.
Changing the arrangement of identical batteries changes the bank's voltage and Ah rating, while the same battery count keeps the ideal nominal energy equal.
The table below compares three ways to arrange four identical 12.8V 100Ah LiFePO4 batteries. Each option contains the same 5.12kWh of nominal energy, but each suits a different system voltage. That is why the Series / Parallel Battery Calculator should be used after you know the voltage required by the inverter, charger, DC equipment, or other system hardware.
| Layout | Bank Voltage | Bank Capacity | Nominal Energy | Typical Planning Goal |
|---|---|---|---|---|
| 1S4P | 12.8V | 400Ah | 5,120Wh | Keep 12V-class equipment and increase runtime capacity. |
| 2S2P | 25.6V | 200Ah | 5,120Wh | Move to a 24V-class bank while retaining two parallel strings. |
| 4S1P | 51.2V | 100Ah | 5,120Wh | Build a 48V-class bank with one series string. |
Start with four 12.8V 100Ah batteries. Two batteries in series create one 25.6V 100Ah string. A second identical series string is built the same way. Connecting the two equal strings in parallel keeps voltage at 25.6V and doubles capacity to 200Ah. Nominal energy is 25.6 × 200 = 5,120Wh.
At 90% planned depth of discharge, battery-side usable energy is 4,608Wh. At 95% system efficiency, estimated delivered usable energy is 4,377.6Wh. A solar installation should then be checked against charging availability with the Solar Battery Bank Calculator.
If the equipment is designed for a 12V-class bank, the same four batteries could be connected as four equal parallel batteries or strings, producing 12.8V 400Ah. The nameplate energy remains 5,120Wh, but current at a given power level is higher than it would be in a 24V or 48V-class system.
That can matter in mobile installations where long cable runs or large inverter loads are involved. For application-specific planning, compare the RV Lithium Battery Calculator or Marine Lithium Battery Calculator before finalizing the bank architecture.
These are planning examples, not testimonials. They show how the same series and parallel rules fit different design goals without implying that one voltage is best for every installation.
If an RV or boat already uses compatible 12V-class equipment, adding approved matching batteries in parallel can increase Ah without changing nominal bank voltage. The design still needs balanced current paths, suitable busbars or cable layout, and protection sized for the available current.
A 2S2P arrangement is useful when a system requires 24V-class hardware but also needs more Ah than one series string provides. The two strings should be electrically equivalent, and each component must support the finished bank voltage and expected current.
A 4S1P layout of compatible 12.8V batteries creates a 51.2V-class bank without parallel strings. Higher system voltage reduces current for the same power, but it also requires equipment rated for that voltage and a battery manufacturer that permits the proposed series connection.
The Series / Parallel Battery Calculator is an arithmetic tool, not an installation approval. Real battery banks are limited by product design, BMS behavior, wiring, protection, temperature, charging, and applicable electrical requirements.
As a conservative generic planning rule, build series strings from batteries that match in nominal voltage, capacity, chemistry, and intended series/parallel capability unless the manufacturer explicitly documents another arrangement. Parallel strings should have the same series count so they share the same nominal string voltage.
Do not assume a battery marketed as “12V lithium” can be placed in unlimited series or parallel groups. Manufacturer limits can be much lower than the calculator's numeric input range. Review the exact battery manual and the Lithium Battery BMS Guide before combining packs.
A larger parallel bank can supply very high fault current. Cable size, lug quality, busbars, fuses, disconnects, and connection symmetry all matter. The generic math here does not calculate those details. For a broader installation checklist, use the site's battery safety section and the wire sizing tool.
Charging equipment must also support the final bank voltage and battery chemistry. A charger suitable for one 12.8V battery is not automatically suitable for a 25.6V or 51.2V bank.
Manufacturer example: Victron's current lithium battery installation guidance documents specific series, parallel, fusing, cable, and balancing requirements for its own products. Treat those numbers as product-specific, not as universal limits for every LiFePO4 battery. Review the Victron installation guidance and its series-versus-parallel overview as examples of the level of detail your battery manufacturer should provide.
The calculator also assumes nominal voltage stays fixed for energy arithmetic. Real terminal voltage changes with state of charge, load, temperature, and chemistry. For voltage interpretation rather than bank configuration, use the Lithium Battery Voltage Chart. For a chemistry-specific energy and runtime estimate, the LiFePO4 Battery Calculator is a better next step.
Use these calculators after you choose a series-parallel layout to check energy, runtime, and conductor planning from different angles.
Convert battery ratings between Ah, Wh, and kWh so you can compare batteries and finished banks at different nominal voltages.
Use CalculatorTake the usable energy from your finished bank and estimate how long it may support a steady load under chosen efficiency assumptions.
Use CalculatorEstimate conductor size from system voltage, current, and distance after you know the battery-bank voltage and expected load current.
Use CalculatorCommon questions about series wiring, parallel wiring, total energy, battery matching, and how to interpret calculator results.
With identical batteries, nominal voltages add while the string's amp-hour capacity remains equal to one battery's Ah rating. Two 12.8V 100Ah batteries in series are therefore modeled as 25.6V 100Ah. The total nominal energy doubles because there are two batteries, not because series wiring creates energy.
With identical batteries or equal compatible strings, nominal voltage stays the same while amp-hour capacity adds. Two 12.8V 100Ah batteries in parallel are modeled as 12.8V 200Ah. Parallel wiring is often used when the system voltage is already correct but more stored energy or runtime is needed.
For the same identical battery count, the ideal nominal watt-hours are the same regardless of arrangement. Four 12.8V 100Ah batteries total 5,120Wh whether arranged 1S4P, 2S2P, or 4S1P. The layout changes voltage and Ah, which changes current behavior and equipment compatibility.
Do not assume mixed batteries are acceptable. Compatibility depends on the battery design and manufacturer rules. For generic planning, matching batteries and equal strings are the clearest approach. If a manufacturer explicitly permits a mixed arrangement, follow its instructions rather than a general calculator assumption.
Multiply one battery's voltage by 2 for the bank voltage, multiply one battery's Ah by 2 for bank capacity, and multiply 2 × 2 for total battery count. With 12.8V 100Ah batteries, a 2S2P bank is 25.6V 200Ah using four batteries, with 5,120Wh nominal energy.
Nominal Wh is a nameplate-style energy calculation. Planned depth of discharge reduces that to the share you intend to use, and efficiency then estimates losses before energy reaches the load. Keeping those inputs separate makes it easier to see which assumption changes usable energy.
No. The Series / Parallel Battery Calculator determines bank voltage, Ah, Wh, usable energy, and battery count. Cable and fuse selection also depends on current, cable length, conductor temperature rating, allowable voltage drop, fault current, equipment limits, and the installation standard or manufacturer instructions that apply.
Verify that every battery is approved for the intended series and/or parallel arrangement, confirm the final bank voltage is compatible with the inverter and charger, check BMS and current limits, plan balanced connections, choose correct conductors and protection, and follow the manufacturer's commissioning and balancing instructions.
Run the Series / Parallel Battery Calculator with your actual battery label, compare 1S4P, 2S2P, and 4S1P layouts, then verify the result against your equipment voltage, manufacturer limits, charging plan, and wiring requirements.
Recalculate Your Bank