Battery Cell Calculator

Calculate total voltage, capacity, and energy for battery packs

Battery Cell Calculator

For various battery chemistries (Li-ion, LiFePO4, NiMH, etc.)

Results:

Total Voltage (V): 0.00

Total Capacity (Ah): 0.00

Total Energy (Wh): 0.00

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How to Use the Battery Cell Calculator

Series Connection (S)

  1. Enter the number of cells connected in series.
  2. Series connections increase total voltage.
  3. Capacity remains the same as a single cell.

Parallel Connection (P)

  1. Enter the number of cells connected in parallel.
  2. Parallel connections increase total capacity.
  3. Voltage remains the same as a single cell.

Cell Parameters

  1. Input the nominal voltage of a single cell (e.g., 3.7V for Li-ion).
  2. Provide the capacity of a single cell in Amp-hours (Ah).

Battery Cell Fundamentals

Series Connection

Connecting cells in series adds their voltages together while keeping the total capacity the same as a single cell. This is used to achieve higher operating voltages for devices.

Parallel Connection

  • Connecting cells in parallel adds their capacities together while keeping the total voltage the same as a single cell. This is used to achieve higher energy storage and longer runtimes.

Key Concepts:

Total Voltage = Cells in Series × Nominal Cell Voltage

Total Capacity = Cells in Parallel × Cell Capacity

Total Energy (Wh) = Total Voltage × Total Capacity

Calculation Formulas

Total Voltage (V):
V_total = S × V_cell

Total Capacity (Ah):
Ah_total = P × Ah_cell

Total Energy (Wh):
Wh_total = V_total × Ah_total

Example Calculation

Battery Pack: 4S2P (4 cells in series, 2 in parallel)

Nominal Cell Voltage: 3.7V

Cell Capacity: 2.5Ah

Total Voltage = 4 × 3.7V = 14.8V

Total Capacity = 2 × 2.5Ah = 5.0Ah

Total Energy = 14.8V × 5.0Ah = 74.0Wh

How to Calculate Battery Cells

These practical steps keep the math straight whether you are designing a DIY powerwall or checking how many 18650 cells you need for a portable pack.

Step 1: Define Target Voltage

Multiply the number of cells in series (S) by the nominal cell voltage to match your inverter or load requirement.

  • Example: 3 series lithium cells × 3.7V = 11.1V pack.
  • Round up the series count to cover voltage sag under load.

Step 2: Note Cell Capacity

Use the rated amp-hour (Ah) or milliamp-hour (mAh) printed on the cell to know how much energy one cell provides.

  • Convert mAh to Ah by dividing by 1000.
  • Record the safe continuous discharge current as well.

Step 3: Size Parallel Strings

Divide the required pack capacity by the single cell capacity to determine how many cells go in parallel (P).

  • Pack Ah = P × Ahcell.
  • Higher parallel count boosts both capacity and current capability.

Step 4: Confirm Energy

Energy in watt-hours is Total Voltage × Total Capacity. This verifies the pack meets runtime expectations.

  • Wh = (S × Vcell) × (P × Ahcell).
  • Add 10–20% margin for inverter and wiring losses.

Step 5: Check Current Limits

Ensure the parallel strings can supply the surge and continuous amps your load needs.

  • Pack current limit = P × cell discharge rating.
  • Use cells with matched age and chemistry to avoid imbalance.

Step 6: Plan Balancing and Protection

Include a BMS that supports the total series cell count and maximum charge/discharge current.

  • Select wiring, fuses, and busbars sized for the worst-case amps.
  • Thermally manage dense packs with airflow or heat spreaders.

Battery Cell Chart

Use this quick reference to mix and match series (S) and parallel (P) counts. Values assume 3.6–3.7V, 2.5Ah 18650 cells and typical efficiencies.

Configuration Series × Parallel Pack Voltage Pack Capacity Energy (Wh) Typical Use
Travel scooter module 3S2P 11.1V 5.0Ah ≈55Wh Compact mobility or drone packs
DIY power tool pack 5S3P 18.5V 7.5Ah ≈139Wh Brushless drills and lawn tools
12V 50Ah Li-ion drop-in 4S20P 14.8V 50Ah ≈740Wh RV house banks or solar carts
Server room backup brick 7S30P 25.9V 75Ah ≈1940Wh 48V UPS modules (with DC-DC stage)
48V e-bike macro pack 13S10P 48.1V 25Ah ≈1200Wh Mid-drive commuter bikes
200Ah solar wall 16S80P 59.2V 200Ah ≈11.8kWh Whole-home storage with inverter

Battery Cell FAQs

Answers to the most searched battery cell sizing and runtime questions.

How long will a 100Ah battery run a 1000W inverter?

Divide the inverter load (1000W) by the system voltage to estimate current, then compare with available amp-hours. On a 12V system that draw is about 83A (1000 ÷ 12). A 100Ah battery theoretically lasts 1.2 hours (100Ah ÷ 83A), but real runtimes drop to roughly 45–60 minutes after inverter losses (10–15%) and depth-of-discharge limits.

How to calculate 200Ah battery?

Multiply the desired pack capacity by the nominal cell capacity to find the parallel count: P = 200Ah ÷ Ahcell. With 2.5Ah 18650 cells you need 80 cells in parallel. Next, choose the series count (e.g., 16S for a 48–60V inverter). The finished pack would be 16S80P, using 1280 cells total.

How to calculate battery cells?

Start with the target voltage to determine series cells: S = Vpack ÷ Vcell. Then size the parallel strings from the required amp-hours: P = Ahpack ÷ Ahcell. Multiply the two to get total cells (Cells = S × P) and verify the resulting energy: Wh = (S × Vcell) × (P × Ahcell).

How many cells is a 11.1 V battery?

11.1V is the standard nominal voltage for a 3S lithium-ion pack using 3.7V cells (3 × 3.7V = 11.1V). The parallel count can vary. A 3S1P pack has three cells, 3S3P has nine cells, and so on, but the series count always stays at three to hit 11.1V.

How many 18650 for 12V 200Ah?

A 12V nominal lithium pack uses four cells in series (4S). For 200Ah you still need 80 cells in parallel when each cell is 2.5Ah. Total cells = 4S × 80P = 320 pieces. Expect about 2.5kWh of energy (12.8V × 200Ah) before accounting for inverter losses.

How many cells are in a 20V battery?

Most 20V (nominal 18–20V) cordless tool packs use five 3.6–3.7V cells in series (5S). Entry-level packs are 5S1P with five cells total, while high-capacity versions use 5S2P (10 cells) or 5S3P (15 cells) to boost amp-hours without changing the voltage.

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