Battery Bank Capacity Calculator
Calculate total Watt-hours (Wh) and Kilowatt-hours (kWh) for your battery bank.
Battery Bank Capacity Calculator
For series and parallel battery configurations
Results:
Total Voltage (V): 0.00
Total Amp-hours (Ah): 0.00
Total Watt-hours (Wh): 0.00
Total Kilowatt-hours (kWh): 0.00
Energy Required (Wh): 0.00
Usable Amp-hours (Ah): 0.00
Nameplate Capacity (Ah): 0.00
Final Capacity w/ Margin (Ah): 0.00
Continuous DC Current (A): 0.00
Recommended OCP (A): 0.00
How to Use the Calculator
Single Battery
- Enter the battery's voltage (V).
- Enter the battery's Amp-hour (Ah) rating.
- Set "Number of Batteries (in series)" to 1.
- Set "Number of Batteries (in parallel)" to 1.
- Click "Calculate" to see Wh and kWh.
Series Connection
- Enter individual battery V and Ah.
- Enter the number of batteries in series.
- Set "Number of Batteries (in parallel)" to 1.
- Total Voltage increases, Ah remains same.
Parallel Connection
- Enter individual battery V and Ah.
- Set "Number of Batteries (in series)" to 1.
- Enter the number of batteries in parallel.
- Total Ah increases, Voltage remains same.
How to Calculate Battery Bank Capacity
Translate load data into a bank size by following these engineering-friendly milestones.
1. Profile the Load
Capture the average power draw (Pavg) and how long it must run.
- List each device and its duty cycle.
- Combine them into a single Pavg number.
- Set the backup window thours.
2. Convert Watts to Watt-hours
Energy drives capacity: Whtotal = Pavg x thours.
- Example: 600 W x 5 h = 3000 Wh.
- Use 24 h for full-day autonomy needs.
3. Find Usable Amp-hours
Normalize to the DC bus with Ahusable = Whtotal / Vsys.
- 24 V system: 3000 / 24 = 125 Ah.
- 48 V system halves the Ah requirement.
4. Apply DoD and Efficiency
Account for chemistry limits and conversion losses.
- Ahnameplate = Whtotal / (Vsys x DoD x ηtotal).
- Lead-acid: DoD ~ 0.5, ηtotal ~ 0.9.
- Lithium: DoD 0.8-0.9, ηtotal 0.93-0.97.
5. Add Design Margin
Multiply by a safety factor to cover aging and unknowns.
- Ahfinal = Ahnameplate x (1 + M).
- Common margin M = 10-20%.
- Round up to the nearest catalog size.
6. Map to Real Batteries
Translate the required voltage and Ah into series/parallel strings.
- Vsys = S x Vbat, Ahbank = P x Ahbat.
- Whbank = Vsys x Ahbank must be >= Whtotal.
- Validate DoD, OCP, and conductor sizing before release.
Battery Bank Capacity Chart
Cross reference common load scenarios with 24 V lead-acid and 48 V lithium banks.
| Avg Load (W) | Runtime (h) | Energy (Wh) | 24 V @ 50% DoD (Ah) | 48 V @ 80% DoD (Ah) |
|---|---|---|---|---|
| 300 W | 4 h | 1200 Wh | ~111 Ah | ~33 Ah |
| 600 W | 5 h | 3000 Wh | ~278 Ah | ~82 Ah |
| 900 W | 6 h | 5400 Wh | ~500 Ah | ~148 Ah |
| 1500 W | 4 h | 6000 Wh | ~556 Ah | ~165 Ah |
| 2000 W | 6 h | 12,000 Wh | ~1,111 Ah | ~329 Ah |
24 V column assumes DoD = 50% and ηtotal = 0.9. 48 V column assumes lithium chemistry with DoD = 80% and ηtotal = 0.95.
Battery Bank Capacity FAQs
Answers to the sizing questions electricians, solar designers, and DIY installers ask most.
How many amp-hours do I need for a 600 W load that runs 5 hours?
600 W x 5 h = 3000 Wh. For a 24 V lead-acid bank at 50% DoD and 90% efficiency, Ahnameplate = 3000 / (24 x 0.5 x 0.9) ~ 278 Ah. Add a 10% margin and specify ~300 Ah.
Why is the usable capacity lower than the nameplate rating?
Depth of discharge limits (to protect cycle life) and conversion losses mean you cannot drain 100% of the printed Ah. Usable Ah = Nameplate Ah x DoD x ηtotal, so a 300 Ah 24 V lead-acid string at 50% DoD provides only ~150 Ah of usable energy.
Should I pick a 24 V or 48 V battery bank?
- 24 V works for smaller inverter loads (<=5 kW) and shorter cable runs.
- 48 V cuts current in half, enabling smaller conductors, higher inverter power, and better efficiency.
- Select the voltage that matches your inverter/ESS listing and conductor limitations.
How many 12 V 100 Ah batteries make a 24 V 300 Ah bank?
Wire two batteries in series to get 24 V (S = 2). Repeat that series pair three times and parallel the pairs (P = 3). The result is Vsys = 2 x 12 = 24 V and Ahbank = 3 x 100 = 300 Ah, or 7.2 kWh total.
Which standards should I review before finalizing the design?
Energy storage systems fall under NEC Article 706 (or 480 for stationary lead-acid rooms). IEC designers reference IEC 62485-2 for stationary batteries, IEC 62619 for lithium cells, and IEC 62933-5-1/-5-2 for ESS siting. Confirm listings (UL 9540/9540A), conductor sizing (NEC 310 / IEC 60364-5-52), and accessible disconnects per NEC 706.15.
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